Experimental &Quasi Experimental Design
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Transcript of 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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