Experimental &Quasi Experimental Design

8/2/2019 Experimental &Quasi Experimental Design

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Dr.(Mrs.) A.V.RamanDean

Omayal Achi College of Nursing

Avadi, Chennai

EXPERIMENTAL DESIGN


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INTRODUCTION TO RESEARCH DESIGNS

Quantitative research design

Research design of a study spells out the

basic strategies that researchers adopt to

develop evidence that is accurate andinterpretable

The research design incorporates some of

the most important methodologicaldecisions that the researchers make

particularly in quantitative studies


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ASPECTS OF QUANTITATIVE

RESEARCH

Intervention

Comparisons

Control of extraneous variables

Timing of data collection

Research sites and settings

Communication with the subjects


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INTERVENTION

In some studies nurse researchers want to test the

effect of specific intervention on dependent

variable (for e.g.. the effect of specific

intervention on labor and neonatal outcome)

COMPARISONThe most common types of comparisons are

1. Comparisons between two or more groups (The

hypothesis that the drug tamoxefin reduced the

rate of breast cancer in high risk women could be

tested by comparing women who received

tamoxefin and those who did not)


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2.In certain instances it is desirable to make

comparisons for the same study participants

(e.g. studying patients heart rate before and afterintervention,

Comparing low back pain for patients lying in

two different positions)

CONTROLS FOR EXTRANEOUS VARIABLES

The complexity of relationships among human

characteristics often makes it difficult to answer

research questions unless efforts are made toisolate key research variables and control other

factors extraneous to the research questions


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TIMING FOR DATA COLLECTION

In most studies data are collected fromsubjects at a single point of time (for e.g.the subjects might be asked on a singleoccasion to describe the health promotionbehavior)

In some designs we contact the subjectsin multiple time (e.g. to observe the growthpattern 3 monthly) Hence the researcher

must decide on the number of datacollection points needed to address theresearch question properly


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RESEARCH SITES AND SETTINGS

sites are the overall location forresearch

Settings are the more specific placewhere data collection will occur

sites and settings to be selected so as tomaximize the validity and reliability ofth data in designing a study. The setting

should be natural and avoid anxietypromoting or foreign to the subjectsexperiences


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COMMUNICATION WITH THESUBJECTS

Decide how much information to begiven to the participants

Full disclosure of the study?

Consent Oral or written?

Think about the reading andcomprehension level of the subjects

Who will provide the information?

What additional questions from thesubjects are expected?

Debriefing sessions?


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EXPERIMENTAL DESIGN

Science answers questions with experiments


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EXPERIMENTAL DESIGN

An experiment is a scientificinvestigation in whichobservations are made and dataare collected according to a setof well defined criteria. In anexperiment, researchers areactive agents not passiveobservers.


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The procedures developedby physical scientists were

profitably adopted by

biologists during the 19thcentury, resulting in many

achievements in physiologyand medicine.


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DEFINITIONExperimental method is an

empirical research method used

to examine a hypothesizedcausal relationship betweenindependent and dependent

variables.


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Begin by asking a question aboutyour topic

One that is testable with thematerials at hand

What is a good question for an

experiment?

DEFINE THE PROBLEM


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Now we need a hypothesis toguide our investigation.

What is a hypothesis?

Your best thinking about how the change

you make might affect another factor.Tentative or trial solution to the question.

An if then statement.


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CHARACTERISTICS OFEXPERIMENTAL DESIGN

A true experimental

design is characterizedby Manipulation,

Control , andrandomization


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Refers to the process by

which the researchermanages the independentvariable in order to study the

effect on the dependentvariable.

MANIPULATION


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EXAMPLE

. Gentle massage is effective as a pain reliefmeasure for elderly nursing home residents

The Independent variable is gentle massage

which could be manipulated by giving somepatients the massage intervention andwithholding it for others

Then it is possible to compare the pain level(dependent variable) in the two group to seeif differences in receipt of the interventionresulted in degree of pain levels


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CONTROL

The experiment must be organized

so that the extraneous factors are

prevented from operating and

confusing the outcome which is

to be appraised.


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Control is acquired by

manipulating by randomizing,by careful preparation of the

experimental protocols, andby the use of a comparisongroup or groups.


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EXAMPLE

If a researcher wanted to supplement diet of

the low birth baby with a particular nutrient

for 2 weeks, the weight gain at the end of 2

weeks would tell us nothing about the

treatment effectiveness

Suppose an average 1 kg. weight gain is

noted does this gain support the conclusion

that nutrition supplement (IV) caused the

weight gain (DV)


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The answer will be NO? because babiesnormally gain weight as they mature

Without a control group- a group that does notreceive the nutritional supplements it isimpossible to separate the effects ofmaturation from those treatment

Therefore the term CONTROL GROUPrefers to a group of subjects whose

performance on a dependent variable is usedto evaluate the performance of theexperimental group on the same dependentvariable


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RANDOMISATIONThe term random essentially means that every

subject has an equal chance of being assigned

to any group. Randomization is the process

that first ensures every unit in the targetpopulation has an equal chance of being

chosen for the study sample, and then

ensures that each unit in the study sample

has on equal chance of being assigned to

either the experimental or the control group.


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EXAMPLE

The effectiveness of a contraceptive healtheducation programme for multiparous

women. Two groups of subjects wereincluded .One group was givenintervention and other was not. Thewomen in the sample are likely to differ

in age, education, and attitude Thiswould affect the woman's diligence inpracticing contraception


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Although randomization is a preferredscientific method for equalizing the

groups, there is no guarantee that thegroup will in fact be equal Therefore weneed a procedure to consciously controlof those characteristics of subjects that

are likely to affect the outcome is calledMATCHING (e.g. if matching were used incontraceptive education, then theresearcher might ensure that if there wasa married 38 year old woman with sixchildren in exp. Group, then there will alsobe 38 year old woman with six children incontrol group


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The antecedent event in a

proposed causalsequence is called the

independent variable.


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The measured effect in

the causal sequence iscalled the

dependent variable.


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Eight classes of extraneousvariablesmay especially interfere with research

on human subjects, history,maturation, testing, instrumentation,

statistical regression selection,mortality and interaction among these.1.History, the specific events occurring

between the first and secondmeasurement in addition to the

experimental variables


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2. Maturation,process within the respondentsoperating as a function of the passage of time

per se (not specific to the particular events),including growing older, growing hungrier,growing more tired and the like

3. Testing,the effects of taking a test upon thescores of a second testing

4.Instrumentation,in which changes in thecalibration of a measuring instrument or

changes in the observers or scores used mayproduce changes in the obtainedmeasurements


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5. Statistical regression, operating where

groups have been selected on the basis of

their extreme scores6. Biaser resulting in differential selection of

respondents for the comparison groups ?

7. Experimental mortality, or differential lossof respondents for the comparison groups

8. Selection-maturation interaction etc.,

which in certain of the multiple group

quasi-experimental designs, might be

mistaken for the effects of the

experimental variable.


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PRINCIPLE GUIDELINES OFEXPERIMENTS

The MAX-MIN-CON. By Kerlinger 1986.

The abbreviation stands for the following.MAX-Maximize experimental variable

MIN- Minimize error variance.

CON-Control extraneous variance.


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MAJOR STEPS INEXPERIMENTAL DESIGN1. Delineate the population or universe to

be studied (i.e. the set of subjects orobjects that share a common observable

characteristic)

2. Select a sample from the population by

random sampling

3. By random assignment, sub-divide thesample into two sub-samples

4 Specify one sub sample the


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4.. Specify one sub-sample, theexperimental group and other the controlgroup

5. Before introducing the independentvariable, observe and record allimportant characteristics of the twogroups

6. Introduce the independent variable intothe experimental group but withholds itfrom the control group

7. After introducing the independentvariable, observe the dependent variablein both experimental and control group

8 Compare the changes that occur in


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8. Compare the changes that occur inthe experimental group with those

that may have occurred in thecontrol group

9. Record the difference

10.Compare these values withstatistically computed values that

judge the significance of the

difference, and indicate whether ornot the observed differences couldhave occurred by chance.


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TYPES OF EXPERIMENTALDESIGN

The investigator planning an experiment

has many experimental design option to

choose. Experimental designs fall into

three major categories.

a)True or classical experimental design

b)Quasi-experimental design

c)Pre-experimental design.


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TRUE OR CLASSICAL EXPERIMENTALDESIGN

TRUE OR CLASSICAL EXPERIMENTAL DESIGN

True or classical experimental designincludes six major designs. They are

Pre-test___ post - test control groupdesign

Solomon four group design After/ post - test __ only experimental

design Factorial design Randomized block design Cross over design or repeated

measures design.


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The most commonly used in nursing studies, arediscussed as nomenclature used and definitionsdeveloped by Campbell and Stanley ( 1963).The standard notations that are helpful

in under standing alternativeexperimental design are -

x To denote the experimental

manipulation. (Treatment orintervention)

O To denote observations ormeasurement

R To denote randomization


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1.PRE-TEST POST-TESTCONTROL GROUP DESIGN

Pretest

Experimenta

lTreatment

Controlgroup

Post

testExperimental

groupRandomassignme

nt

Pretest Posttest


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EXAMPLE

Effectiveness of antenatal

nutrition education on

pregnancy and labor outcome

among primi para mothers

attending out patient departmentof selected hospitals Madurai

2007-2009


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2. Solomon four group design is acomplex particularly useful in studies of

developmental phenomena and permits theinvestigator to differentiate many effects.

Pretest

Experimental

Treatment

Controlgroup

Experimental

group

Controlgroup

Post testExperimentalgroup

Randomassignment

Pretest Post test

ExperimentalTreatment

Post test

Post test


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EXAMPLE

Effectiveness of workshop on

management of HIV to improve

the nurses attitude toward

patients with AIDS admitted in

selected hospitals , Madurai2006-2008


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3.Post- test only control groups designthis design, which is sometimes called after only controlgroup designs, is composed of two randomly assignedgroups, but neither of which is pre tested or premeasured in the before period of time.

Control

group

Post

-test

Post

-testExperimental

group

Experimental

treatmentRandomassignment


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EXAMPLE

Effects of holding the newborns onpaternal bonding behavior

The researcher randomly assigned 36

first time fathers attendinguncomplicated deliveries of normalinfants to experimental and controlgroup (Those who held and did not

hold their infants at delivery)12-36hours after the babies were bornbonding behavior frequencies were

recorded and observed the outcome


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4. Factorial design

In this design testing of multiplehypotheses is done in a single experiment

In factorial experiments subjects are assignedat random a specific combination of

conditionse.g. Does auditory stimulations have a more

beneficial effect on the development ofpremature infants than tactile stimulation?

(effect is weight gain and cardiacresponsiveness)


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EXAMPLE

AUDITORY

A1

TACTILE

A215 Min

B1

A1 B1 A2 B1

30 Min.

B2

A1 B2 A2 B2

45 Min.

B3

A1 B3 A2 B3

Type of stimulation

Daily

Exposure


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5. Randomized Block Design

There are two factors (independent

variables) but one factor is notexperimentally manipulated.

e.g. Compare the effects of tactile

versus auditory stimulation for femalevs male infants.

It can be structured as 2x2 experiment,

with type of stimulation as one factorand gender as the other factor


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6. Cross over design (orRepeated

measures design)It involves the exposure of the same

subjects to more than one experimental

treatmente.g. Effectiveness of two alternative

back rest position ( flat, horizontal vs.

30o elevation) on intracranial and

cerebral perfusion pressures in brain

injured adults


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PRE-EXPERIMENTAL DESIGNS

1. The oneshot case study orsingle case study

The study design has a totalabsence of control, it is

considered to be little value asan experiment.


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2.One-GroupPretest-posttest

design

Only one group is observed before

and after the independent variableis introduced. Loss of the controlgroup decreases the usefulness

of the study but may be necessaryin cases where it is not possibleor feasible to have control groups


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EXAMPLE

Effectiveness of selected

nursing intervention onknowledge and level of

satisfaction among clientswith stroke


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ADVANTAGES OF EXPERIMENTAL

DESIGN

1.True experiments are the most powerful

method for testing hypothesis of cause and

effect relationship between variable because of

the rigours, precision and control properties ofexperimental design.

2. This ifthen type of relationship is important

to nursing and medical researchers because ofits implications for predication and

explanation.


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3.Though the control imposed

by manipulation comparison

and randomization,

alternative explanation to acause interpretation can be

ruled out or discredited.


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DISADVANTAGES OF EXPERIMENTALDESIGN

1. Some variables are not feasible or ethicalto manipulate e.g., assessing pregnantwomen to take a new drug found to bedangerous to fetal development would

not be ethically possible.2. Randomization and otherwise equal

treatment of control and experimentalgroup can occur in a laboratory, but these

conditions do not resemble what goesunder real world conditions, andexperimental findings can therefore bebased on rather artificial circumstance


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3. Experimental design attempt to

reduce variable to measurableterms. Many of the phenomena thatare important to science in nursing

are complex, multidimensional andholistic, and defy the reductionismthat has worked reasonably in thephysical or natural sciences.


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QUASI EXPERIMENTALDESIGN


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DEFINITION

It is a research design in

which the researcher initiates

an experimental treatment butsome characteristics of a trueexperiment is lacking.


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PURPOSES

To provide alternative means ofexamining causality in situations

not conducive to experimentalgroup.

To facilitate the search for

knowledge and examination ofcausality in situations in whichcomplete control is not possible.


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RANDOM ASSIGNMENT

It is a procedure used toassign subjects to

treatment or controlgroups randomly.


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COMPARISON GROUPS

Comparison groups are not selected using

random sampling and do not receive theexperimental treatment.

Types of comparisons groups:

Groups that receive no treatment.Groups that receive placebo treatment

Groups that receive usual treatment.

Groups that receive second experimentaltreatment.


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TYPES OF QUASI EXPERIMENTALDESIGN.

QUASI

EXPERIMENTALDESIGN

Interruptedtimes series

design

Non equivalentcontrol group

design


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NON EQUIVALENT

COMPARISONGROUP DESIGNS

1 ONE GROUP POSTTEST ONLY


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1. ONE GROUP POSTTEST ONLYDESIGN

It is referred to as pre-experimental ratherthan quasi experimental where manipulation ofIndependent variable is done and posttest isconducted to measure the outcome.

Manipulation of

Dependent variable

Treatment

Measurement of

Independent variablePost test

Example

Outcome of Antenatal Education on pregnancy andlabor .

2 POSTTEST ONLY DESIGN WITH A


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2. POSTTEST ONLY DESIGN WITH ACOMPARISON GROUP

In this design a comparison group is introducedto determine the efficacy of the treatment and aftermanipulation of independent variable only posttestis conducted.

Treatment

Experimental Group

Post test

Treatment

Non equivalent control group

Post test

Introducing Computer education to improve staff morale

3 O G P P D i


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3. One Group Pretest-Posttest Design

In this design the experimental group is

expected to serve as a comparison group. Pretestand posttest scores are used to find the efficiencyof the treatment.

Experimental Group

Pre-test Treatment Post test

Effectiveness pelvic floor muscles exercises in

control of incontinence of urine.

Effectiveness of infection control policy to

decrease infection in postnatal ward.


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4. PRE-TEST & POSTTEST DESIGNS WITHA COMPARISON GROUP

In this design the comparison groupis not randomly selected. Theanalysis is made on examining the

differences between comparisongroup and experimental grouppretest, between pretest and post

test, between comparison group andexperimental group posttest.


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Experimental group

Pre- test Treatment Post-test

Non equivalent control group

Pre-test Post-test

Example:

Effectiveness of education on partograph in

assessing labour progress among nurses

working in labour rooms

INTURRUPTED TIME SERIES DESIGN


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INTURRUPTED TIME SERIES DESIGN

It is similar to descriptive time series design

except that a treatment is applied at s givenpoint in time and the outcome is measured atdifferent point of time In simple interruptedtime series design there is no control or

comparisongroup

Use of multiple methods to measure theoutcome greatly strengthenthe design.

Experimental groupPre-test T Post test

O(1)O(2) O(3) o(1) o(2) o(3)

EXAMPLE


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EXAMPLE

Effectiveness of selected nutritionalinterventions on growth anddevelopment pattern of childrenattending under fives clinic at

Omayal Achi community health centreat Tiruvalluvar district 2006- 2008


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Interrupted Time series designs witha comparison group

Comparison group allows examination ofdifferences in trends between groups afterthe treatment and of the persistence of

treatment effects overtimeExperimental group

Pre-test T Post test

o(1) o(2) o(3) o(1) o(2) o(3)

Comparison groupPre-test T Post test

o(1)o(2) o(3) o(1) o(2) o(3)

ADVANTAGES & DISADVANTAGES OF


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ADVANTAGES & DISADVANTAGES OFQUASI EXPERIMENTAL STUDIES

Advantages:From the point of view of controls for

internal validity quasi experimentaldesigns are thought to be superior to pre

experimental design.Disadvantages:

Cannot test causal hypothesis

Do little to ensure external generalizability.


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Experimental &Quasi Experimental Design

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