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Confidentiality and statistics on grids

Vilni Verner Holst BlochMSc. landscape ecology and natural resourcesStatistics NorwayOtervegen 23N - 2225 KongsvingerTel : ++47 / 62 88 50 62 Fax : ++47 / 62 88 50 97 E-mail : vvh@ssb.no

A proposal on common rules for handling confidentialityto the Board of Confidentiality

at Statistics Norway

The European Forum for Geostatistics workshop in Haag, Netherlands 5th – 7th of October 2009

“bridge the gap” between theory and practice in GeoStatistics

Session 1: Small area statistics

Bjørn ThorsdalenPopulation StatisticsStatistics NorwayOtervegen 23N - 2225 KongsvingerTel : ++47 / 62 88 50 62 Fax : ++47 / 62 88 50 97 E-mail : vvh@ssb.no

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Overview of the presentation

• Background

• System of grids for national statistics

• Examples on confidentiality issues

• Different confidentiality rules

• Examples on use of todays confidentiality rules

• Guidelines for grid statistics

• Further work

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Background

• A) Requests from users(insurance companies, scientists, companies with localisation or marketing issues, general public, education puposes)

• B) Internal drive within Statistics Norway (coming GIS and censuses)

• C) Partnership in National INSPIRE Forum (obligations)

• D) New possibilities(better presentation of spatial statistics, spatial analysis etc)

The more users need, and we produce, the more crucial common rules for confidentiality becomes

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4

Norwegian Mapping

andCadastreAuthority

FIREWALL

Geodatabase

Statisticalbase

registers Statistics

Statistics N

orway

ArcGIS coverages,shape files

etc.

WMS ssb.no

Statbank

ExternalWMS/WFSproviders

Local

Copy

”Wall of confidentiality”

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Statistical grids for Norway

Grid name Cell size Number of cellsSSB100m (1) 0.01 km2 35 000 000 cellsSSB125m (1) 0.01 km2 20 000 000 cellsSSB250m (1) 0.0625 km2 5 600 000 cellsSSB500m (1) 0.25 km2 1 400 000 cellsSSB1km 1 km2 350 000 cellsSSB5km 25 km2 15 000 cellsSSB10km 100 km2 5 000 cellsSSB25km (2) 625 km2 500 cellsSSB50km (2) 2 500 km2 150 cellsSSB100km (2) 10 000 km2 40 cellsSSB250km (2) 62 500 km2 10 cellsSSB500km (2) 250 000 km2 4 cells

(1) Because of limitations in many software packages and for practical use, these grids are recommended as grids with a county coverage.

(2) These grids might also cover sea territories. Number of cells refers to coverage of Norwegian mainland. One has however to be aware of deviations in grid cell areas for regions remote from the Norwegian mainland and Svalbard.

http://www.ssb.no/english/subjects/01/90/doc_200909_en/doc_200909_en.pdf

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Number of farms. 1x1km. 1999

1 – 3 farms 4 or more farms

Confidentiality examples

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Building stock. 100x100m. 2007.

1 – 3 buildings 4 or more buildings

Confidentiality examples

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Night time population. 1x1km. Year 2000 over 2008.

1 – 9 persons 2000 10 or more 2000 1 – 9 persons 2008 (new settlements) 10 or more 2008 (new settlements)

Confidentiality examples

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Confidentiality examples

Number of enterprises. 1x1km. 2008

1 – 3 enterprises 4 or more enterprises

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Leisure homes. 1x1km. 2008.

1 – 3 leisure homes 4 or more leisure homes

Confidentiality examples

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Night time population. 1x1km. Year 2008 over 2000.

1 – 9 persons 2000 (abandond cell) 10 or more persons 2000 (abandond cell)

Confidentiality examples

120 10 20 30 40 50 60 70 80 90 100

Ant personer i ruter med færre enn 4 personer

Ant personer i ruter med færre enn 11 personer

Ant personer i ruter med færre enn 31 personer

Ant personer i ruter med færre enn 51 personer

Ant personer i ruter med færre enn 101 personer

Ruter med færre enn 4 personer

Ruter med færre enn 11 personer

Ruter med færre enn 31 personer

Ruter med færre enn 51 personer

Ruter med færre enn 101 personer

1000 m 250 m 100 m

Confidentiality examplesNumber of grid cells and inhabitants by grid cell sizes. Per cent.

Share of grid cells with less than N persons

Share of persons in grid cells with less thanN persons

N > 101

N > 51

N > 31

N > 11

N > 4

N > 101

N > 51

N > 31

N > 11

N > 4

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Fordeling av jordbruksbedrifter på 1x1km ruter. 2008.

0

2 000

4 000

6 000

8 000

10 000

12 000

14 000

16 000

18 000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Antall jordbruksbedrifter i 1x1km rute

Ant

all j

ordb

ruks

bedr

ifte

r

Confidentiality examples

Frequency of agricultural enterprises by 1x1 km grid cells.2008

Grid cells by number of agricultural enterprises

Nu

mb

er o

f ag

ricu

ltu

ral e

nte

rpri

ses

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• Previous and existing rules for handling confidentiality on grids are not adequate.

• Confidentiality rules should be handled at lowest reasonable geographical level.

• Official statistics should not be given at all geographical levels/grid sizes.

• One should have a set of limits/treshold values dependent of the sensibility of the topics for statistics or quality of sources for statistics.

Recommondation given to the Board of Confidentiality at Statistics Norway

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• The following has been recommended to the Board

Recommondation given to the Board of Confidentiality at Statistics Norway

1. Total figures (persons, enterprises, buildings, dwellings) and non-sensitive variables (age, sex, building type, NACE code) do not need to be anonymised.

2. Statistics on sensitive variables can be given if total figures exceed threshold values. Threshold value is to be set by responsible department for each statistics, dependending on quality, sensitivity and details. Threshold values are fixed to total figures of 10, 30 or 50. No further anonymisation is done.

3. Grid sizes of 125mx125m and 500mx500m shall not be used for official statistics.

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• Work within the Geostat to make guidelines for handling confidentiality issues

• Adoptation of European rules for handling confidentiality in grid statistics ?

Further work

Thank you for your attention