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The Cardiff Consumer Panel: Methodological Aspects of the Conduct of a Long-Term PanelSurveyAuthor(s): Neil Wrigley, Cliff Guy, Richard Dunn, Larry O'BrienSource: Transactions of the Institute of British Geographers, New Series, Vol. 10, No. 1 (1985),pp. 63-76

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63

h e

C a r d i f f

C o n s u m e r

P a n e l

methodologic l

s p e c t s

o

t h

o n d u t

o

long term

p n e l

s u r v e y

NEIL

WRIGLEY,

Lecturern

Geography,Dept

of

Geography,

University

f

Bristol,

BristolBS8

1SS

CLIFF

GUY,

Lecturern

Town

Planning,University f

WalesInstitute

f

Science nd

Technology,

Colum

Drive,

Cardiff

CFI 3EU

RICHARD DUNN,

Lecturer

n

Geography,Dept

of

Geography,

University

f

Bristol,

BristolBS8

ISS

LARRY

O'BRIEN,

Lecturer

n

Geography, ept

of

Geography,

College f

St

Pauland St

Mary,

CheltenhamGL50

2RN

RevisedMs received October1984

ABSTRACT

Panel

surveys

can

providehigh

quality

data of

unmatchable etail.

They

are of central

mportance

or the

description

andanalysisof spatialbehaviourwhich nvolvesrecurrenthoice andmovement,and for the assessment f change n

behaviourover time.

In

this

paper

a

discussionof some

methodological

spects

of

panel

surveys

s

provided

via a

description

nd

appraisal

f the

design,

conductand

characteristicsf

the

CardiffConsumer

anel

Survey

of

1982.

The

importance

f the

database

generated

y

the Cardiff

urvey,

as

a

resource

or

geographical

esearch,

s

assessed.

KEY

WORDS:

Longitudinal/Panel

urveys,

Consumer

anel,Spatial

behaviour,

Retail

change,

Shopping

diary,

Panel

attrition,

anel

ecruitment,

ata

quality

ontrol

INTRODUCTION

Issues which concern

the

design

and

conduct

of

panel

surveys

are

generally

less well known to

geographers

than

those

which relate to cross-

sectional

questionnaire

surveys.

However,

the

infor-

mation

obtained

from

longitudinal

surveys

of

this

type

is of

central

importance

for the

description

and

analysis

of

spatial

behaviour

which involves

recurrentchoice and

movement,

and for the

assess-

ment of

change

in behaviour over

time. In

this

paper

we

discuss some

methodological

aspects

of the

conduct

of

panel

surveys

focusing

on a

recently

con-

ducted

long-term panel

survey

of

urban

shopping

behaviour in

Cardiff.

Although

a

wide

range

of

longitudinal survey

designs

are

commonly

referred to

as

panel

surveys,

in

this

paper

we

adopt

the

definition

of

panel

sur-

veys

typically

encountered

in

consumer

researchand

concentrate

upon

the richest

possible

longitudinal

design

in

which a

complete

history

of the

sequence

and

timing

of

events

is

collected. A

central

charac-

teristic of such

survey

designs

is that

they

normally

involve

continuous

monitoring

of the

process

under

study

(in

our

case

shopping

behaviour)

and,

to

achieve

this,

panel

members

are

usually

asked

to

Trans. nst. Br.Geogr.N.S. 10: 63-76 (1985) ISSN: 0020-2754

Printedn GreatBritain

8/11/2019 622250

3/15

NEIL

WRIGLEYT

AL.

record all

relevant

aspects

of their

behaviour

in some

form of

diary.

For

this reason

such

surveys

have

often

been

referred to as

diary

surveys

by

geogra-

phers

and

planners.

In

panel

surveys,

all

the usual

elements of

cross-

sectional survey design and conduct remainimport-

ant

issues

(sample design,

questionnaire

layout,

interviewer

technique,

response

and

non-response

error

identification,

and so

on)

but,

in

addition,

considerable attention must

also be

given

to

panel

recruitment,

to

the reduction of

panel

attrition,

to

panel

remuneration,

and

to the

maintenance of

data

quality

over

long

monitoring

periods.

These

are

some

of

several

methodological

issues

which are

considered

in

this

paper.

Before

doing

that,

however,

it is

important

to

preface

the

methodological

discus-

sion

by

a

consideration of the

motivations

which

lead to the

instigation

of the Cardiff

panel

survey

of

1982.

In

essence,

three

major

factors

combined to

suggest

that the

early

1980s was

an

appropriate

ime

for a

new and extensive

panel

survey

in a

British

city.

First,

during

the

previous

twenty years

there had

been

major

changes

in

the

British

grocery

retailing

industry.

The

substitution of

capital

for

labour

in

the

industry,

the

increasing

scale

of

retail

units,

the

decline

of

resale

price

maintenance,

the

growth

of

'own-brand'

rading

and the concentration of market

share

amongst

a

smallerand smallernumber

of

firms,

had

resulted in and/or

accompanied

the

rapid

growth

of

major

retail

corporations

such as

Sainsbury's,

Tesco's and Asda. The

increasing pro-

ductivity

and

healthy

(sometimes

spectacular)

growth

of

profits

of

these

firms,

even

in

periods

of

economic

recession,

had

provided

continued

(often

enthusiastic)

Stock

Market

support,

and

had

helped

to

finance

major

investment

programmes

by

the

leading

firms. In their

turn,

these

programmes,

and

a

somewhat more

liberal attitude

by

planners

to the

development of edge-of-city superstores,had trans-

formed the face

of

grocery retailing

and

significantly

altered

typical patterns

of

shopping

behaviour

for a

large

proportion

of the

population

of Britain.

Accompanying

these

changes

there had also been

a

major

shift

in the balance

of

power

in the

industry,

away from

the manufacturers

of

grocery

items

and

towards

the

rapidly expanding

retail

corporations.

Indeed,

this shift

in

power

had

progressed

so far that

the

relative

positions

of manufacturers

and retailers

had

almost

completely

reversed

from those

typical

in the

early

1960s.

By

the

early

1980s,

the

major

retail

organizations

were often in a

position

to dic-

tate the

price

levels at

which

manufacturers

supplied

items

and

to

significantly

affect the

success of the

manufacturers

leading

(and

nationally

advertized)

brands

by

their

stocking

policies.

Secondly, despite these major changes and the

rapid

increase in the

size of the market

analysis

and

store

location research

units

of

the

large

firms,

there

was

a

surprising

dearth of

up-to-date

information on

the

characteristics of

shopping

behaviour

in

the

United

Kingdom.

Most

of

the information which

was

available

tended either o be tied to the needs of

the

manufacturer ather

than

the retailer and to lack

adequate

locational

information

for

retail

analysis

and

forecasting

purposes,

or to

be

rather

dated.

Thirdly,

the

potential

benefits

to be

gained

from

the

analysis

of

panel-data

had

significantly

increased

in the late 1970s and

early

1980s. In

part

this reflec-

ted the

growth

of

computing

power

and

storage

capabilities,

so that the

very

large

amounts

of

data

which

panel

surveys

typically

generate

became

much

more

straightforward

o handle.

Perhaps

more

important,

however,

was the fact that the

analysis

of

panel

data

had become a

major

research area in the

late

1970s

across a wide

range

of

disciplines,

includ-

ing

econometrics,

sociology, marketing,

statistics

and

transportation

research,

and

some of these

developments

were

beginning

to be

applied

to

geographical problems

which involved

movement

and

repeated

choice

(Pickles

and

Davies,

1984;

Davies and

Crouchley,

1985).

The

potential

thus

existed to

develop

a

new

generation

of methods of

retail

analysis

and

forecasting

based

upon panel-

data

models of urban

shopping

behaviour

(see

Goodhardt

et

al.,

1984)

and it was felt that these

would

provide important

practical

tools

for retailers

and urban

planners.

The three factors described above

provided

the

rationale

for

a

new

and extensive consumer

panel

survey

oriented to the needs

of

geographers,

plan-

ners and retailers,and which would contain detailed

locational information

on all

aspects

of

grocery

shopping

behaviour.

It

was

hoped

that the

survey

would

provide

a

major

resource

for

understanding

the

nature

of urban

shopping

behaviour

in

Britain

n

the

1980s,

the scale

and

type

of

change

in

such

behaviour since the

1960s

and

early

1970s,

and

for

the

development

of a

new

generation

of methods

for

retail

analysis

and

forecasting.

The Cardiff

survey

was

designed

to meet these

requirements

and

was

conducted

over the

period

January

o

July

1982.

It is

believed to be the most

comprehensive panel

survey

64

8/11/2019 622250

4/15

Methodological

spects

f

theconduct

f

a

long-term

anel

urvey

of urban

shopping

behaviour

ever

carried out

in

the

United

Kingdom,

and the

data

from

the

survey

are

now

available to

all researchers

via the

ESRC

Data

Archive

at

the

University

of Essex.

In

this

paper

a

description

and critical

appraisal

of

the design, conduct and characteristicsof the Cardiff

Survey

is

presented.

It

should

be

stressed

that the

paper

does not contain

analysis

of

the

survey

data as

such

results

are

presented

elsewhere

(e.g.

Wrigley

and

Dunn, 1984a,

b,

c, 1985;

Dunn

and

Wrigley,

1984a, 1985;

Dunn et

al., 1983;

Guy,

1983, 1984;

Guy

and

O'Brien, 1983;

Wrigley

et

al.,

1984).

Instead it seeks

to answer

a

series

of

methodological

questions

which

are central

to

any

evaluation

of the

Cardiff

Consumer

Panel data

as a resource

for

geographical

research.

THE CARDIFF

SURVEY

At

the

completion

of

the Cardiff Consumer

Panel

Survey,

continuous

records

on all

aspects

of

daily

food

and

grocery shopping

had been obtained

for

454 households

over

a 24-week

period

(January

o

July

1982).

The basic

unit for these

records was

the store

visit,

and for

each visit

to an

individual

store made

by

a

panel-household,

the

following

information was

obtained:

-the

name and location of the

store,

-the

time,

day

and date of the

visit,

-mode

of

transport

to

the

store,

-shopping trip

origin,

and store 'tour'

infor-

mation

(i.e.

subsequent

destinations

on same

shopping

trip),

-a

list

of

products purchased

at

the

store,

-the brands

of certain

products

purchased,

-total

expenditure

on food and

grocery pro-

ducts at

the

store,

-total

expenditure

on

non-food/non-grocery

products

at

the

store,

-an identificationof whether the store visit was

made

by

the

panellist,

other

household mem-

ber,

or non-household

member.

In

addition,

a

wide

range

of

socio-economic,

demo-

graphic

and attitudinal

information was obtained

describing

each

panellist

and his/her

household,

plus

a

more

limited,

but

extremely

useful,

range

of

infor-

mation

on

typical

store

prices

during

the

survey

period.

The

basic information

on

each

store visit was

reduced to

one

(sometimes two)

computer-records

of

80 characters. For

the

24-week

period

this

amounts to

a

total

of

83

548

computer-records,

covering

expenditure

of more than

?4

million,

and

visits

to

over

1000

different

stores.

In

the

period

of two

years

since

the data from the

Cardiff

survey

became

available,

they

have been

used to

develop

and test

new methods of

retail

analysis and forecasting and to study the following

diverse

topics:

-patterns

of

repeat

buying

at individual stores

(Wrigley

and

Dunn, 1984a;

Dunn

et

al.,

1983);

-multi-store

purchasing patterns

and the

incidence

of store

switching

(Wrigley

and

Dunn,

1984b);

-the interaction

of

store-choice

and brand-

choice

(Wrigley

and

Dunn,

1984c);

-the

relationship

between

household

income

and

shopping

behaviour

(Guy,

1983);

-Sunday

and

late-night

shopping

(Wrigley

et

al.,

1984);

-the

degree

and

pattern

of

loyalty

to

grocery

stores

(Dunn

and

Wrigley,

1984a);

-the

nature

of

multi-stage

and

multi-purpose

shopping

journeys,

and the

identification

of

shopping

activity

bundles

(Uncles, 1985);

-the market

performance

of

particular

stores

or

store

groups

(Guy

et

al.,

1984;

Dunn and

Wrigley,

1984b);

-the

usage

of

edge-of-city

and

within-city

superstores

(Guy,

1983, 1984;

Dunn and

Wrigley,

1985);

-comparison

of the

shopping

behaviour of

women

holding

full-time,

part-time,

or no

paid

employment

(Uncles,

1984);

-comparison

of the

shopping

behaviour of

the

unemployed

and

employed

in

a

period

of

recession

(Guy,

1985);

-the

analysis

of

home-shopping,

including

mobile traders and

tele-shopping

(Uncles

and

Ducatel,

1984);

-changes

in

shopping

trip

characteristics

since

the

early

1970s

(Broom

and

Guy,

1983;

Uncles,

1985).

Furthermore,

we

expect

these studies

to

be

only

a

small

part

of

the

retailing

and consumer research

which will

be

based

on

this

data base over

the next

five to ten

years,

and a number of further

projects

are

currently

under

way

including

a

NSF-funded

cross-cultural

comparison

of

British

and American

consumer

spatial

behaviour,

using

a

slightly

modi-

fied

version

of the Cardiff

panel

survey

design

in

California

(Golledge

and

Wrigley,

1983).

In

addition,

it is

already

apparent

that

the

data

base is

being

utilized

for the

purposes

of basic model

65

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5/15

NEIL

WRIGLEY

ETAL.

TABLE

.

Characteristics

f

some

eographical/planning

onsumer

anel

urveys

Panel

Panel

Length

Study

Location

Size

(weeks)

Garrison

t

al.

(1959)

Cedar

Rapids,

USA

262

4t

Marble

Bowlby

1968)

Cedar

Rapids,

USA

116

4

Davies

1973)

Coventry,

UK

487

1

Rogers

1974)

Peterborough,

K

172

4

Hudson

1975)

Bristol,

UK

89*

10

Hanson

Hanson

1980)

Uppsala,

weden

296

5

Wrigley

1980)

Bradford,

K

102 20

O'Kelly

(1981, 1983)

Hamilton,

Canada

704

2

Daws McCulloch

(1974)

Watford,

UK

1672

1

Bruce Mann

1977)

North

London,

UK 1707

1

Bullock

t

al.

(1974)

Leicester,

K

450*

1

Guy

et al.

(1983)

Cardiff,

K

454

24

*all

panellists

were students

tmost analyses

performed

n

99 households over 2 weeks

development

and

testing

by

a number of social

scientists

(e.g.

Halperin

et

al., 1984;

Dunn and

Wrigley,

1985;

Davies

and

Pickles,

1985).

The Cardiff

survey

differs from

previous

con-

sumer

panel

surveys

in two main

respects.

First,

in

contrast

to commercial

consumer

panel

surveys

in

the

United

Kingdom

run

by

organizations

such as

Audits of Great

Britain,

Attwood

Statistics,

British

Market

Research

Bureau,

and Mass

Observation

(UK) Ltd,

it contains

detailed

locational

nformation

on consumer travel and

purchasing

behaviour

which

the

commercial

surveys

typically

do

not

collect

and/or

report.

Secondly,

compared

to

previous

con-

sumer

panel

surveys

carried

out

by

geographers

or

planners,

and which do

provide

detailed

locational

information,

it covers

a much

longer period

(six

months)

which

is of

a

similar

length

to that

encountered

in commercial

surveys.

In

contrast,

as

shown

in Table

I,

previous

geographical/planning

surveys

have

tended to be

rather restricted

in

terms

of

length

of

monitoring period

and/or

panel

size.

THE PANEL ACCOUNTING

EQUATION

To introduce

several

of the

important

issues

of

panel

survey methodology

use is

made of the

following

equation:

Number

f

recruitment

ate

/

attrition ate

households

x x

1-

sampled

100

100

Number f

Final

panel

-

non-continuous

used

for

reporters

analysis

which we

term the consumer

panel

accounting

equa-

tion. The

key

parameters

in the

equation

are the

recruitment rate and attrition rate. The

recruitment

rate

is

defined

as the

percentage

of households sam-

pled

who

agree

to become members

of the

panel.

The attrition rate

is

defined as

the

percentage

of

households

who,

having

joined

the

panel,

fail to

remain members

of it

for

the

full

monitoring

period

(24

weeks

in the Cardiff

survey).

Also,

panellists

who

leave the

panel

for some

specified length

of

time,

and thus become what

are termed 'non-

continuous

reporters',

are

usually

excluded

from

the final

panel

used for

analysis

for

reasons

of

consistency.

Fig

1

gives

a

diagrammatic

representation

of

the

process

of

obtaining

the final

panel

and

intro-

duces certain terms

used in

the

paper.

In

the

Cardiff

survey

2012 households were

sampled

using

a

multi-stage

stratified random

design.

Of

these,

775

were

not

contacted

or refused

to answer

a short

'initial'

questionnaire

(for

details

see

below).

Of

the

1237 who were contacted and who also completed

the 'initial'

questionnaire,

605

agreed

to

become

members of the

panel (representing

a recruitment

rate of 30

per

cent)

and 632

(termed

the

'non-panel-

lists')

refused.

The

group

of 605

'panellists'

represents

the

starting

size

of the

panel.

Of

these,

481 remained members

of

the

panel

for the

full

24-week

monitoring

period

and

124

dropped

out

(representing

an attrition rate

of 20

per

cent).

Those

who failed

to

remain

members of the

panel

we

term

'drop-outs'

and those who

remained we

term

'stayers'.

Finally,

the

records

of

27

'non-continuous

66

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6/15

Methodological

spects

f

theconduct

f

a

long-term

anel

urvey

Note :

figures

refer to the Cardiff

consumer

panel.

FIGURE .

Stages

n

the

process

of

obtaining

consumer

anel

reporters'

were

removed from the data files

leaving

a

total of 454 'continuous

reporters'

whose

purchasing

records constitute the

final

panel

data set used

for

analysis

purposes.

TARGETS AND

PILOT SURVEY

Initial

targets

and

estimates

The first

step

in

any

panel

survey

is to

specify

a

target

for

the size of

the

final

panel.

In the Cardiff

survey

the

target

was

a

panel

in the

range

450-500

households

providing

continuous records of

grocery

purchasing

over

24

weeks. The

number of house-

holds which must

be

sampled

to meet such a

target

depends upon

three

criticalfactors:

1

the

assumed recruitment

rate;

2 the

assumed attrition

rate;

3 the

likely

number of

'non-continuous

reporters'.

Closely

related to

these three factors

are the

questions:

a

how best to

design

a

'diary'

within which

infor-

mation on

purchasing

behaviour

will be

recorded;

b how best to administer the survey to maintain

the

quality

of the

data.

The first

estimates

of recruitment

rate

and

attrition

rate for the

Cardiff

survey

were 58

per

cent

and 30

per

cent

respectively.

These

figures

were

based

upon

consultation

with

appropriate

com-

mercial

firms and

comparison

with

previous

surveys.

However,

because the nature of

the Cardiff

survey

was

significantly

different

from

previous

studies,

a

detailed

12-week

pilot

survey

was undertaken to

test

these

assumptions.

The

pilot

survey

was

also

extremely

valuable in

improving

the

layout

of the

diary

in which

the

panellists

recorded

the

infor-

mation on their

purchasing

behaviour,and in

testing

the

survey

administration and data

quality

control

procedures.

Overall,

the

importance

of this

pilot

sur-

vey

cannot be

overstressed

and some brief

details

are

necessary

(Wrigley

and

Guy,

1981).

Pilot

survey

In the

pilot

survey

90

randomly

selected

households

in

two sub-areas of

Cardiffwere

sampled,

and a

32

per

cent

panel

recruitment rate was

achieved. In

terms

of

Fig

1,

there

were

29

panellists,

47

non-panellists,

and 14

non-contacts or

refusals

to

answer the 'initial'

questionnaire.

The

pilot

survey

thus

had a

substantially

lower

recruitment rate

than

originally

envisaged

and it

highlighted

the

arduous

nature of

this

stage

of

a

long-term

consumer

panel

survey.

It also

emphasized

that

in

the main

survey

the

recruitment

stage

must be

carefully

prepared

and

adequately

costed,

and should

not be

rushed

in

any

way.

The

pilot

survey

ran

for 12

weeks

(September

to

December,

1980)

during

which

time

only

three

of

the

29

panellists

dropped

out;

an

attrition rate

of

only 10 per cent. This suggested that there was little

support

for a

pessimistic

view of a

very

high

attrition rate in the main

survey,

and that

the initial

estimate of

30

per

cent for the

attrition

rate over 24

weeks was

high

rather

than

low.

On the basis of

these results

revised

estimates

of the

recruitmentand

attrition

rates

to be

expected

in

the main

survey

were

made;

these

were 38

per

cent

and 25

per

cent

respectively.

This

suggested

that

about 1800

house-

holds

needed to

be

sampled

at the

first

stage

of

the

main

survey

if

the

target

size

of the

final

panel

was

to be

achieved

successfully.

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NEIL

WRIGLEYTAL.

The

pilot

survey

also

provided

an

important

opportunity

to

test

the

survey

administration,

panellist/fieldworker

control,

and

panel

remunera-

tion

procedures

to be

used

in

the

main

survey,

and

to make several

improvements

to

the

design

of the

weekly diary of grocery shopping behaviour (the

basic

data

collection device in

the

Cardiff

survey).

In

the latter

context,

particular

attention was

given

to the

layout

of

the

diary,

to

the

elimination of

any

possible

ambiguities,

and

to the elimination

of

any

response

bias which

might

be caused

by

the

adoption

of

a

particularordering

of

the list

of

product

categories

used to record

purchases.

MAIN

SURVEY: RECRUITMENT

PHASE

Sample

design

The

choice

of

Cardiff

as the location of the consumer

panel

had

been

fixed at the

outset,

largely

for

prag-

matic

reasons,

being

of suitable

size,

convenient for

both

principal

investigators,

and

offering

a suffi-

ciently

heterogeneous

range

of retail

opportunities,

housing

types

and

social sub-area

characteristics. n

addition,

it also offered considerable

potential

cost

savings

associated with

the

availability

of

prior

research on

the

retail structure of

the

city,

and

because

an

experienced

commercial

market research

firm,Research and Marketing (Wales and the West)

Ltd,

which

the

principal investigators hoped

to

employ

to conduct the

survey,

was located

in

the

city

and thus could

operate

at

substantially

lower

unit

costs.

The

experience

of

previous

commercial

surveys

and

of

the

pilot

survey

indicated that considerable

advantages

were to be

gained

by

clustering

panel-

households.

This

reduced

between-panellist

journey

times

for

the

fieldworkers,

and

helped

lessen the

considerable

problems

associated with

attributing

a

unique

numerical code to each store visited

by

the

panellists.

As a

result,

panel-households

were selec-

ted from 8 sub-areas of north

and

east

Cardiff

(see

Fig

2)

via

a

multi-stage

stratified

random

design.

The 8 sub-areas included a

wide

variety

of

housing

types

within

both the

private

and

public

sectors

of the

market,

and

were

representative

of

a

range

of

locational,

accessibility

and socio-economic

conditions.

Recruitment

rocedures

On

the basis of

the

pilot

survey

results,

the

estimated recruitment

and

attrition rates

for the main

survey

indicated that

approximately

225 households

should

be

sampled

in each

sub-area

(a

total of

1800

households)

to

produce

a final

panel

size of

450-500.

In

the

event,

panel

recruitment

n

January

1982 proved to be even more arduousthanhad been

expected,

primarily

because of the worst snowfalls

for

50

years

and the

subsequent paralysis

of the

transport

system

of

the

city.

Thus,

in four sub-areas

the

number

of households

sampled

had to be

increased

slightly, leading

to the final

figure

of 2012

households

sampled

(see

Fig

1)

and

a final

recruit-

ment

rate of 30

per

cent.

The households

sampled

within each

sub-area

were

pre-selected using

a random

design,1

and three

visits were made

at different times of

day

before

a

household

was defined

as a

non-contact.

If

contact

was made with a

household,

a short interview

(termed

the 'initial

questionnaire')

was

completed,

if

possible,

with the

principal

food and

grocery

shop-

per.

This contained

a

small number

of

questions

on

the

socio-economic

and

demographic

composition,

and

shopping

habits,

of the

household.

It

served two

important purposes:

a

to

establish

the credentials of

the

fieldworker

and a

relationship

with the

respondent.

A

blunt

request

from

a

stranger

(or

by

letter)

to become

a

panellist,

without

any

prior

discussion,

would

have

almost

always

been

unsuccessful;

b

to

provide

basic

information about

panellists

and their

households,

and to allow

comparisons

to

be

made between

panellists

and those unwil-

ling

to become

panellists

(the

so-called

'non-panellists'-see

Fig

I

and discussion

below).

On

completion

of the

interview,

the

respondent

was

asked if he/she would

be

willing

to

help

with

diary

completion

'over

the next few

months'.

Those

willing

to

participate

were revisited

the

following

week,

and as

many

as

possible

were

recruited

to the

panel. At that time, the process of diary completion

was

fully

explained,

and it was

emphasized

that

a

small

payment

(?4)

would

be made

every

four

weeks

if the diaries had been

completed properly

over that

period.

Once

the

respondent

had

agreed

to

participate

he/she was

given

the first

diary,

various

notes

to

help

diary

completion,

and

a

folder

of

information

about

the

survey.

The

following

week,

all

panellists

were

revisited so that the

first

week diaries

could

be collected

and

checked,

and

arrangements

or

subsequent

fortnightly

fieldworker

visits

were

made.

68

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Methodological

spects

f

the

conduct

f

a

long-term

anel

urvey

Key

to

District

Centres

1

Countisbury

Avenue

2

Maelfa 3

Leo's,

Splott

4

Albany

Road

5

Crwys

Road

6

Whitchurch Road 7

Merthyr

Road

8

Cowbridge

Road

East

9Clare

Road

10

Hoel-y-deri

FIGURE

.

Location f

study

areas n

Cardiff

MAIN

SURVEY:

MONITORING

PHASE

The

'running-in'

eriod

The

standard

commercial

practice

in

long-term

con-

sumer

panel

surveys

is to

have a

'running-in'

period

before the

start

of the main

monitoring

period.

In

the

Cardiff

survey

a

two-week

'running-in'

period

was

used,

during

which

period

panellists

completed

diaries

but for

which the

information

obtained

was

not

coded

or

used

for

analysis

purposes.

This

period

allowed

the

fieldworkers

to

check

through

the

first

completed

diaries

with the

panellists

in

detail

and

to

point

out

and

correct

any idiosyncratic

recording

errors

before

such erroneous

practices

became

established.

In

addition,

these diaries

were

checked

in

detail

by

supervisory

staff

at Research

and

Marketing

Ltd so that fieldworker

deficiencies

could

also be

corrected.

69

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NEIL

WRIGLEY

TAL.

This

'running-in'

period proved

to

be

an

immen-

sely

useful

adjustment

period

in

which initial

problems

could be

overcome,

the

composition

of

the

panel

could be

finely

tuned

(a

small number of

panellists

were also recruited

in this

period),

and

supervisory systems could be tested. It is the firm

belief of the authors that

such

periods

offer

major

benefits in

panel

surveys,

(i)

in terms of

improving

data

quality

and

panel composition,

and

(ii)

because

they

allow

the researcher to avoid

unnecessary

(and

expensive)

coding, editing

and

computer

file

creation

for the substantial

number of

panellists

who

can be

expected

to leave the

panel

within

the

'running-in' period,

often after

having

produced

low

quality

information for

just

a

few

days.

(Such

panellists

are termed 'immediate

drop-outs'

and we

compare

their

characteristics

o the

'later

drop-outs',

'stayers'

and

'non-panellists'

below).

Attrition

rate

As noted

above,

the

attrition rate in

the main

survey

was

20

per

cent

(better

than

estimated)

and

Fig

3

summarizes

the

pattern

of

panel

attrition

over

time.

This

graph

follows

the

classical

pattern

with

a

large

number of

drop-outs

in the

'running-in'

period

and

in the

early

weeks

of the

main

monitoring

period.

In

fact,

62

per

cent

of

panel

attrition

had taken

place

by

the

end

of

the first week

of the main

monitoring

period, and from the third week onwards the

average

weekly

loss was

only

1-7

panellists.

Techniques

f

attrition ontrol

The rate of attrition

achieved

in

panel

surveys

is

directly

related to the

attention devoted to

the

issues of

panel

recruitment,

panel

control,

panel

remuneration

and fieldworker

control. In the

original

design

of the Cardiff

survey

considerable

care

was devoted to

these

issues,

and

the

pilot

survey

confirmed

their

importance.

In

summary,

six

points

appear

to

be

important

if

panel

attrition is

to be

kept

to a minimum.

The

frequency

and

nature

of

visits

by

fieldworkers

to

panel

members The Cardiff

survey

adopted

a

fortnightly

pattern

of

fieldworker

visits to collect

diaries,

and

panellists

retained

the same

field-

worker

throughout

the

survey.

This

pattern

of visits

involved the use

of 15 fieldworkers

and was

expens-

ive,

but

it

was

vital to the success

of

the

survey.

Panellists soon build

up

a

relationship

with

their

fieldworkers which then

serves to

reduce

attrition

significantly.

In

addition,

fieldworkers

play

an

Running-in

I

pe,iod

,

2

4

6

8 10 12

14 16

18

20

2 24

Week

number

FIGURE. The

pattern

f

panel

attrition ver

time

important

educational role

(especially

in the

early

stages

of the

survey)

and if

they

arewell trained and

controlled

this

significantly improves

the

quality

of

the

diary

information

obtained.

The

design

and

time

span

of

the

diary

The

layout

of

the

diary

should

make it

as

easy

as

possible

for

panellists

to

supply

the

required

information,

and

in

this

respect

a number of

improvements

were

made

on the basis

of reactions

from

panellists

to the

diary

used

in

the

pilot

survey.

A

second

important

factor

was the

decision

to use

weekly

(rather

than

fortnightly

or

monthly)

diaries.

Again,

this increased

the cost

of the

survey

but it:

(i)

resulted

in a

diary

that

was

less

daunting

in

size;

(ii)

allowed

more

effective office

control,

includ-

ing

a week

by

week

checking

of

attrition

rates,

quality

of

reporting,

and

panellist

or

fieldworker

problems;

(iii)

reduced the

risk

of

'slippage'

in the com-

pletion

of the

diary by

the

panellists,

result-

ing

in undesirable

'completion

by

recall',

or

possibly

withdrawal

from

the

survey.

Careful

panel

recruitment

by

trained

and

experienced

fieldworkers

As noted

above,

the

recruitment

phase

is

arguably

the most arduous

phase

of

such

surveys.

It is

a

phase

that

should not

be

rushed

in

any way,

and

which

must

be

carefully

prepared

and

adequately

costed. Once

again

the

main

survey

benefited

considerably

from

the

experience

of the

pilot

survey.

Suitable

panel

remuneration

nd incentives

Previous

studies

have shown that

cash rewards

to

panel

70

600-

580-

E

560-

-6540-

ai

Z

520-

500-

480-

8/11/2019 622250

10/15

Methodological

spects

f

theconduct

f

a

long-term

anel

urvey

members

undoubtedly

reduce

panel

attrition. In

the

Cardiff

survey

panellists

received

?4

at

the

end of each

four

week

period

for

which

diaries had

been

successfully

completed,

plus

a ?1 bonus for

remaining

on the

panel

for the

full 24

weeks.

Whilst

such limited financial ncentives did not retainpanel

members

who

had become

seriously

disaffected,

they certainly

influenced

marginal

cases

and,

perhaps

more

importantly,

gave

the

majority

of

panellists

the

sense

of

doing

a

job

which was

'valued'.

An additional incentive was

provided

in the form

of

a

series

of

letters

from Research

and

Marketing

Ltd

(see

Guy

et

al.,

1983).

These

explained

the

purpose

of the

study,

encouraged panellists

to

remain to

the end of the

monitoring

period

once

they

were

three-quarters

of the

way

through,

and,

in

general,

encouraged

them

to

take

an interest

in

participation.

Fieldworker

control In

long-term

panel

surveys

there

is

a

danger

that

fieldworkers

as

well

as

panel

members will

begin

to lose

interest,

and that

the

quality

of the

survey

will

begin

to decline. For this

reason,

it

is

essential

that

fieldworkers

are

closely

supervised

and

generally encouraged

throughout

the

survey

period.

In the Cardiff

survey

fieldworkers

were

supervised

by

Researchand

Marketing

Ltd and

were

in

regular

and

frequent

personal

contact with

the fieldwork supervisor and office staff. Completed

diaries were examined

by

the

office

staff,

and

each

fieldworker

was

given

lists of the

remaining

errors made

by

his/her

panellists.

In

this

way

data

quality

was

continuously

monitored and maintained

through

a

process

of

supervisor/fieldworker/

panellist

feedback.

The

services

of

a

professional

market

research

organization

Long-term

panel

surveys

demand

a

large

number

of

trained

and

experienced

fieldwor-

kers, supervisors,data coders, processing controllers

and

so

on.

The

Cardiff

survey

benefited

considerably

from the

services

of a

professional organization

which had the

necessary

expertise

and

experience

in

this

area,

and

which was

committed to

the

require-

ments of an

academic

project.

In

terms of cost-

effectiveness and data

quality

the location

of this

organization

within

the

study

area itself was also

extremely

important.

In the authors' view this use

of

a

professional organization

is essential to the

success

of a

long-term

panel

survey.

Although

it

may,

at

first,

appear

to

be

unnecessarily

expensive,

it will

generally

be uneconomic

and

inefficient to

attempt

to

take on such

a

task

'in-house' and

to

attempt

to

set

up

such

an

organization

for the

purposes

of a

single

academic

project.

Thesecondquestionnaire

During

the

middle weeks

of the

main

monitoring

period

those households who

were still members

of

the

panel

were

asked

to

complete

a

much

more

detailed

questionnaire

relating

to their

demographic

and

socio-economic characteristics

and

their

attitudes

to

shopping

(for

further details

see

Guy

et

al., 1983,

pp.

89-108).

Since certain

types

of

analysis

of the

panel

data

require

information derived

from

this

questionnaire

(for

example

the

relationship

between observed

shopping

habits and household

characteristics),

high

response

rate

was

essential.

In

the

event,

a

response

rate of 98

per

cent was

achieved,

which was

largely

due to the

timing

of

the

questionnaire.

By

the middle weeks of the

main

monitoring

period

most

panellists

had

developed

a

personal

commitment to their

fieldworker,

were

taking

an active interest

in

completing

their

diaries,

and were thus

willing

to

fill in an additional

questionnaire.

In

addition,

a

further

small cash incen-

tive was

offered to

panellists

for

their

participation

in

the second

questionnaire.

Supplementarynformation

Given

the

large

costs

and

long

start-up

times

involved

in

mounting

a

long-term

consumer

panel

survey

it

is

important

that smaller

lower-cost

proj-

ects be co-ordinated with

the main

monitoring

period.

In

the Cardiff

survey,

the two

most

import-

ant of these

were

a

survey

of

grocery

prices

in

stores

frequented

by

the

panellists

(Guy

and

O'Brien,

1983),

and the collection of information on stores

visited

by

the

panellists,

including

details

of

owner-

ship,

store

type,

exact

location,

goods

sold,

and

floorspace

(see

Guy

et

al.,

1983,

pp.

126-33,

155-57).

In

addition,

a

careful

scrutiny

of the

local

press

was maintained for

any

events

likely

to influence

shopping

behaviour,

such as

major

promotions

involving

stores

in

Cardiff,

incidents

affecting

accessibility

to

shopping

centres,

and the

opening

or

ownership

changes

of stores.

In

fact,

such events did

take

place

during

the main

monitoring

period

of the

survey

and this

type

of

supplementary

information

may

be

important

in

suggesting

research

topics

and/or

in the

interpretation

of

certain

aspects

of

recorded behaviour.

71

8/11/2019 622250

11/15

NEILWRIGLEYETAL.

REMOVAL

OF

NON-CONTINUOUS

REPORTERS

The

standard

commercial

practice

is to

remove

for

analysis

purposes

those

panellists

who

have

'unacceptable'gaps

in

the

continuity

of

their

pur-

chasing

records.

However,

there

is little concensus

on the

definition of

'unacceptable',

except

that

absences of

occasional

days,

weekends

or

periods

of

less

than

a week are

acceptable.

In

these

situations,

the

panellists

are

likely

to

adjust

their

weekly

pattern

of

purchasing

to

compensate

and can be

regarded

as

just

'not

buying anything'

on

the

days

of

absence.

In the

Cardiff

survey,

detailed records

were

kept

for

each

panel

member of

diaries

satisfactorily

completed,

days

of

holiday

taken,

missing

diaries,

and

so on. At the end of

the

monitoring

period

the information was summarizedin the form of a

panellists-by-week

matrix,

and

'continuous' and

'non-continuous'

reporters

were identified

using

the

most

rigorous

approach

in

current commercial

prac-

tice

(plus

the

addition of certain extra more

stringent

criteria-see

Guy

et

al.,

1983,

pp.

134-38 for

details).

On

this

basis,

27

panellists

were defined as

'non-continuous'

reporters

(in

most

cases because

they

took

an annual

holiday

of more than 15

days

during

the

monitoring

period).

This left

a

panel

of

454 'continuous'

reporters,

82

per

cent

(371)

of

which

had no absences of

more

than

seven

days

and

41 per cent (185) of which had not even a single day

away

from home

during

the

monitoring

period.

One of the

major

factors

influencing

the number

of non-continuous

reporters

is

clearly

the

timing

of

the

survey

in

relation to

major

holiday

periods.

In

the

UK,

the

optimum

timing

for

a six-month

panel

survey

is thus from

January

to

early July

since this

avoids the

major

holiday

periods

of

Christmas

and

late-July/August.

Shorter

term

panels

will also

benefit from

avoiding

these

periods

and other less

important

ones such as Easter.

DATA

QUALITY

Human

geographers

familiar

with the

response

and

non-response

error

problems

of

cross-sectional

or

short-term

panel

surveys may, initially,

find it rather

difficult to

accept

that the

quality

of data

supplied

in

long-term

panel

surveys

can be

maintained

over

lengthy monitoring

periods.

They

may

believe

that

panellists

will

rapidly

become

bored

by

the task

and

will thus

supply poor

quality

or even fabricated

data,

that fieldworker

motivation/performance

may

decline,

and that

the sheer size of the task will

inevitably

result in

larger

error

problems

than nor-

mal

at the data

editing/coding,

file creation

stage.

Essentially,

there are two

types

of

response

to such

beliefs.

First,

the

procedures

adopted

to maintain

data

quality

can

be

exposed

to critical

appraisal.

Second, summary measures of the information

obtained from

the

panel

can

be

compared,

for con-

sistency,

to the

results of other

surveys

and

analyses.

Techniques

f

quality

control

The

procedures

necessary

to maintain

the

quality

of

data

supplied

by

the

panellists

over

a

long

monitor-

ing

period,

and to maintain fieldworker motivation/

performance,

are

essentially

those

required

o reduce

panel

attrition

(discussed above)

and

they

need

not

be

repeated

here.

They

are

matters

which

must be

reviewed

in

detail,

and

on

which decisions must be

taken,

at the

design

stage. During

the course of the

survey,

data

quality

is

maintained

by

implementing

these

procedures

as

rigorously

as

possible,

but

with

sensitivity

at all times to the

crucial issues

of

fieldworker-panellist

contact

and fieldworker-

supervisor

control.

Overall,

there is

simply

no

sub-

stitute for a team of

experienced,

well-briefed and

highly

motivated

fieldworkers who

visit

panellists

and check their

diaries

at

least

every

fortnight,

and

who are backed

up

by

a

supervisory

system

which

monitors their

performance,

provides

the

necessary

advice

and

encouragement, and maintains con-

tinuous feedback from office

to

fieldworkers to

panellists

and vice versa.

Whatever

the

procedures adopted,

however,

and

despite

all the

efforts

of

the

fieldworkers,

t is inevit-

able that

occasional

response

errors

(incorrect

recording,

omission of

information,

over-reporting

and

so

on-see

Sudman,

1964)

will occur.

Neverthe-

less,

there is no evidence that

the

magnitude

of these

errors

is

any

greater

in

well-conducted

long-term

panel

surveys

than in cross-sectional or short-term

panel

surveys.

As

Ehrenberg

1972,

p.

8)

has noted:

Panel membersbecome

experienced

n

keeping

their

records

f

they

continue o

co-operate,

nd t

seems

that

the efficientand

satisfying

way

of

filling

out

a

diary

eachweek s to

try

anddo so more

or less

correctly.

Of

course,

there

will

always

be

a

small

number

of

panellists

who

persistently

provide

what

are

obviously

inadequate

records

of their

shopping

behaviour.

However,

such

panellists

are

readily

iden-

tified and can be

removed from the

panel

by

the

supervisory

staff.

In

the

Cardiff

survey, only

seven

72

8/11/2019 622250

12/15

Methodological

spects

f

theconduct

f

a

long-term

anel

urvey

panellists

were

dropped

from the

panel

during

the

main

monitoring period

for this reason.

A

further

eature of the

quality

control

procedures

adopted

in

the Cardiff

survey

which

is

particularly

worthy

of

note,

was

the decision to sub-contract

the

transfer of edited and coded diaries to computer

tapes

to a

separate

and

specialized computing

firm

(DCMS

Ltd)

with

greater expertise

in the

design

and

implementation

of

large

error

checking

routines.

This decision enabled more than 30

consistency,

range

and

logic

checks to be

specially

designed

and

to be

performed

at the

point

of transferof the edited

and coded diaries to

computer tapes.

As

such,

it

provided

a

complementary

and

independent

level

of error

detection

to that

performed

in-house

by

Research

and

Marketing

Ltd

during

the

diary

editing

and

coding stages.

Errors

identified

by

DCMS

Ltd

were

reported

back to the staff of Research and

Marketing,

who

then

returned

to

the

original

diary

to check matters

of detail.

Any

amendments

which

were

then found

to be

necessary

were made to

both

the

computer tapes

and the

original

diaries.

Overall,

a

relatively

high

proportion

of the

budget

of

the

Cardiff

survey

(when

compared

to

previous panel

surveys)

was

allocated to

the error

checking process.

However,

it is

the

authors' view

that extensive and

specialized

error detection

systems

of this

type,

although

expensive

to

design

and

operate,

are

vital

to

the success of

complex surveys

which

produce

very

large

amounts

of

data.

Consistency

hecks

In commercial market research

there is

a

long

tra-

dition of

checking long-term

consumer

panel

data

for

consistency

against

other

sources,

such as retail

audit

and

factory

shipment

figures

and

against

data

from ad

hoc cross-sectional

surveys.

Indeed,

Ehrenberg

(1972,

p.

9)

has

argued

that

consumer

panel

data

are often

'amongst

the most

fully

checked

and

reproducible

that

are

available

in

the social

sciences'.

In

the Cardiff

survey,

two

types

of

consistency

checks have

been

performed.

The first

type

has

involved the

comparison

of

descriptive

statistics

obtained from the

Cardiff

survey

against

similar

measures obtained from other

contemporary

sources. For

example,

the

relationship

between

household income and food and

grocery expendi-

ture exhibited

by

the

Cardiff

panel

has

been

shown

to be

very

similar to that revealed in the

Family

Expenditure

Survey

of

1981

(Guy,

1983).

The second

type

of

consistency

check has con-

cerned the

predictability

of

a

number of

important

indices of consumer

purchasing

behaviour.

In

this

context,

it

has been shown that a

family

of models

widely

used in the statistics and

marketing

literature

to

study

brand

purchasing

behaviour

can

success-

fully predict,not only importantaspects of the brand

purchasing

behaviour

of

the

Cardiff households

(Wrigley

and

Dunn,

1983),

but also similar ndices of

purchasing

patterns

at individual stores

(Dunn

et

al.,

1983;

Wrigley

and

Dunn, 1984a,

b).

The

excellent

fit of

these models indicates that the Cardiff data

reveal the same

type

of

purchasing

regularities

as

previously

found

in a

wide

range

of

studies

in a

number of countries. As

such,

these

results

provide

considerable

support

for the

validity

of the Cardiff

data. The alternative

would

be

to believe that

panell-

ists within

a

wide

range

of

independently

con-

ducted

surveys

with different

designs

and different

operating procedures

could

somehow

produce

low

quality

(or

even fabricated

data)

in such a

way

as

to

consistently

produce

the

same

predictable

regularities

n

the internal

relationships

of

brand

and

store

purchasing

patterns-surely

a

very

difficult

belief to

support.

REPRESENTATIVE

NATURE OF

THE PANEL

Human

geographers sceptical

of

the

value of

con-

sumer

panel

data

often

question

whether

individuals

who are

prepared

to

take

part

in such

surveys

are in

some

way

different from

non-participants.

A

feature

of the Cardiff

survey

was that

its

design

allowed

some answers to

this

question

to

be obtained.

As

Fig

I

shows,

of the

initial 2012

households

sampled

in the

Cardiff

survey,

775 were not

contac-

ted or

refused to

answer the 'initial'

questionnaire,

and there

is

no

information

on

this

group

(other

than

knowledge

of sub-area in

which

each

non-contact/

non-respondent

is

located,

and the

approximate

numberof adults in each household).2 At this stage,

representativeness

of the

sample

must

rely

upon

the

fact that a

stratified

random

sample

design

was

used,

that three

attempts,

at

different

times of

day,

were made to contact

each

household,

and

that well-

trained and

experienced

fieldworkers

were used.

Certainly,

any

bias in the

representative

nature of

the

panel

which

may

have

arisen at this

stage

is not a

feature of

panel

survey

methodology per

se

but is

a

common

problem

of

all

social

surveys,

both

cross-sectional and

longitudinal.

Once initial

contact with

the

princi-al

food

73

8/11/2019 622250

13/15

NEILWRIGLEY

TAL.

and

grocery shopper

of a household had been

established, however,

that contact had to

be

con-

verted,

if

possible,

into successful recruitment to

panel membership.

At

this

stage

the first

potential

bias

in the

representative

nature of the

sample

which

is directly attributable to the panel survey

methodology

occurs. At

this

stage,

632 contacts

refused

to

join

the

panel.

A

comparison

of

the

characteristics

of these

'non-panellists'

with

the

605

panellists

successfully

recruited,

and

using

data from

the

'initial'

questionnaire

completed

by

both

groups,

revealed

that

non-panellists

were

slightly

more

likely

to be

in the

age

category

55

plus,

from small

households,

and

to be male

(though

it

should be

noted that

overall

only

12

per

cent of

principal

ood

and

grocery

shoppers

were

male).

In

addition,

car

ownership

was lower

amongst

non-panellists.

Of

course,

the

initially

recruited

panel

is not the

final

panel,

and

it

may

be the case that those

panel-

lists who

'stay

the course' are different from those

who

drop

out

during

the

monitoring

period.

This

may

reinforce

or,

alternatively, may

counteract the

potential

bias to the

representative

nature of

the

panel

introduced

at the

previous

stage.

Using

infor-

mation from

the 'initial'

questionnaire

a

comparison

of

the 124

panellists

who

dropped

out of the

panel

during

the

monitoring

period

with

the 481

panellists

(the

'stayers')

who

remained,

was conducted.

This

revealed that

stayers

were

much more

likely

to

be

aged

25-44 and also members of

car-owning

households.

Approximately

twice

as

many

'stayers'

(32

per

cent)

as

'drop-outs'

(17

per

cent)

fell

into

this

category.

In

contrast,

'drop-outs'

were

dis-

proportionally

from

non-car-owning

households

and

aged

16-24 or 45

plus.

A further

breakdown

of the characteristics

of the

drop-outs

can

be obtained

by

dividing

them into

two

groups:

'immediate

drop-outs'

who left

the

panel

during

the

'running-in'

period,

and 'later

drop-outs'

who left

the

panel

during

the

main

monitoring period. A comparison of these two

groups

revealed that

'immediate

drop-outs'

were

much more

likely

to be older

(79

per

cent were

aged

45

or

over)

and

to be members

of

non-car-owning

households than was

the case for either

'stayers'

or

'later

drop-outs'.

In

contrast,

'later

drop-outs'

were

very

similar

to

'stayers'

in

most

respects,

with

the

one

minor

exception

that

'later

drop-outs'

were

more

likely

to

be

in

the

youngest age group,

16-24,

than

was the case for either

'stayers'

or

'immediate

drop-outs'.

On the basis of these

comparisons

it would seem

that

the Cardiff

panel

(and

we

suspect

long-term

panel

data in

general)

is

to

a

limited extent biased

towards

family

units in

which

the

panellist

is

aged

25-44.

Moreover,

these families tend to be

car-owners

and

are, therefore,

more mobile and

possibly more affluent.In addition, it would appear

that 'immediate

drop-outs'

who leave the

panel

during

the

'running-in'

period

are in some

respects

an

exaggerated

version

of

non-panellists

whereas

'later

drop-outs'

are

very

similar

to

stayers.3

This

pattern

of

over- and

under-representation

of

sub-

groups

must be borne in mind when

using

the data

for

certain inferential

purposes

or

to

draw

policy/

urban-planning

conclusions,

and

appropriate

correc-

tions

can,

where

necessary,

be made.

However,

the

degree

of bias should not

be

over-exaggerated,

for

the results of the much more detailed 'second

questionnaire'

show that the final

panel

of con-

tinuous

reporters

used for

analysis

purposes

includes

substantial numbers

of

virtually

every

type

of

population

sub-group

used

in the

description

and

analysis

of urban

shopping

behaviour

(including

the

old,

the

immobile,

the

unemployed,

and so

on).

Also,

it

in no

way

precludes

extremely

valuable com-

parisons

of the Cardiffresults with

those of

previous

short-term or

long-term

panel

surveys

reported

in

the

literature

of

geography, planning,

marketing

and

statistics

(including

the

government-financed

National Travel

Surveys),

as

these

surveys

are

likely

to be

subject

to similar imited

patterns

of

sub-group

over-

and

under-representation.

As

such,

the

Cardiff

data

provides geographers

with

an

immensely

useful

resource

for

understanding

the nature and

scale of

the

significant changes

in

shopping

behaviour

in

the

United

Kingdom brought

about

by

the

factors

described

in the introduction

to

this

paper.

CONCLUSIONS

It is our

belief

that

well-designed

and

rigorously

conducted panel surveys can provide high-quality

data of unmatchable

detail.

Moreover,

because

of

the recent

rapid

methodological

advances

in

panel-data

analysis,

such

data can be used to

provide

answers

to

a

range

of

problems

which

remain

ntrac-

table in the

presence

of conventional cross-sectional

data. In this

paper

we

have shown how

it is

possible

to collect

high-quality,

locationally

detailed,

infor-

mation from

a

panel

survey,

even when

the monitor-

ing

period

of the

survey

extends

over

a much

longer

time

horizon

than

that

typical

of

previous

geographical/planning

panels.

74

8/11/2019 622250

14/15

Methodological

spects

of

the conduct

f

a

long-term

anel

survey

The rich

geographical

data base

provided

by

the

Cardiff Consumer

Panel

provides

a

unique

and

valuable resource

for

understanding

the nature of

urban

shopping

behaviour

in Britain in the

1980s,

and

for

understanding

the scale

and nature

of the

changes in such behaviour which have accompanied

the

transformation

of

the

British

grocery retailing

industry.

The

large

volume of research referred to

above,

either

completed

or still

in

progress,

gives

some indication of the

possible

uses of the

Cardiff

data.

We

hope

that this

paper

may

encourage

other

interested researchers to

exploit

the data base via

the

ESRC

Data

Archive,

and

that

it

will

encourage

both the

application

of

panel

data

techniques

in

urban

geography/planning

and a wider debate on

appropriate

survey

methodology.

ACKNOWLEDGEMENT

The

Cardiff Consumer

Panel

was

funded

by

the

Economic

and Social Research Council

under

grant

D00230010.

NOTES

1.

Households

n

each sub-areawere selected

by

random

sampling

of the

1981-82

electoral olls.

To

give

each

household

n

a

sub-area n

equal

chanceof

being

selec-

ted,

a

procedure

known as

'firsting'

Hoinville

and

Jowell,1978)

was

adopted

o correct or the fact

hatan

electoral

oll is not a

roster

of

householdsbut

a

list of

electors

those

eligible

to

vote,

i.e.

those

18

years

old

or over

approximately)

ho come fromhouseholds

f

varying

ize.As a

result,

he number f adults

18

years

old

or

over)

in

each of the 775

non-contact/

non-response

ouseholds

s known.

2.

See

1

above.

3. This

provides

an

additional

ustification

or

having

a

'running-in'

eriod,

and it should

be

noted

that the

similarity

between the

'later

drop-outs'

and

'stayers'

can be

exploited

by

those researchers

ho,

for some

analytical

urposes,

may

wish to

supplement

he size of

the final

panelby drawing

n the

incomplete

ecords

f

the 'later

drop-outs'.

REFERENCES

BROOM,

D. and

GUY,

C. M.

(1983)

'Accessibility

nd

mobility

as

determinants f

shopping

behaviour'.

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