EXPERIMENTAL DESIGN
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EXPERIMENTAL DESIGNEXPERIMENTAL DESIGN
Experimental and Pre (Quasi) Experimental and Pre (Quasi) Experimental DesignsExperimental Designs
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Basic Issues in Experimental Basic Issues in Experimental DesignDesign
Manipulation of the Independent VariableManipulation of the Independent Variable
Selection of the Dependent VariableSelection of the Dependent Variable
Assignment of subjects (or other test units)Assignment of subjects (or other test units)
Control over extraneous variablesControl over extraneous variables
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Manipulation of the Independent Manipulation of the Independent VariableVariable
In a classical experiment, the researcher In a classical experiment, the researcher measures the condition of the subjects – measures the condition of the subjects – both treatment and control groups - on the both treatment and control groups - on the dependent variable and then dependent variable and then “manipulates” the independent variable for “manipulates” the independent variable for the “treatment group” while not the “treatment group” while not “manipulating” that variable for the “manipulating” that variable for the “control” group, and then “re-measures the “control” group, and then “re-measures the dependent variable for both groups while dependent variable for both groups while controlling “all other variables”.controlling “all other variables”.
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Laboratory vs Field ExperimentsLaboratory vs Field Experiments
Artificial – Low Artificial – Low RealismRealismFew Extraneous Few Extraneous VariablesVariablesHigh ControlHigh ControlLow CostLow CostShort DurationShort DurationSubjects Aware of Subjects Aware of ParticipationParticipation
Natural – High Natural – High RealismRealismMany Extraneous Many Extraneous VariablesVariablesLow ControlLow ControlHigh CostHigh CostLong DurationLong DurationSubjects Aware of Subjects Aware of ParticipationParticipation
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““ONE-SHOT” CASE STUDYONE-SHOT” CASE STUDY
T1T1 T2T2 T3T3
XX OO
Where: Where: X = TreatmentX = TreatmentO = ObservationO = Observation
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How good is this research design?How good is this research design?
Scientifically it is not good at allScientifically it is not good at all– However, that the classical case studies in all of the social However, that the classical case studies in all of the social
sciences have contributed more to those discipline’s knowledge sciences have contributed more to those discipline’s knowledge than any other designthan any other design
First – much of the pioneer work that shaped the social First – much of the pioneer work that shaped the social sciences was accomplished before the advent of sciences was accomplished before the advent of sophisticated research designssophisticated research designsSecond –research is always the enterprise of individuals Second –research is always the enterprise of individuals and individual skill can “substitute” for sophisticated and individual skill can “substitute” for sophisticated design controlsdesign controlsThird – research designs which require sophisticated Third – research designs which require sophisticated controls are limited to different kinds of inquirescontrols are limited to different kinds of inquires
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““ONE-GROUP”ONE-GROUP” PRETEST - POSTTEST PRETEST - POSTTEST
T1T1 T2T2 T3T3
OO XX OO
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““STATIC GROUP” COMPARISONSTATIC GROUP” COMPARISON
T1T1 T2T2 T3T3
XX OO
OO
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““PRETEST - POSTTEST”PRETEST - POSTTEST”CONTROL GROUP DESIGNCONTROL GROUP DESIGN
T1T1 T2T2T3T3
TrtTrt OO XX OO
CtrlCtrl OO OO
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Posttest-Only Control GroupPosttest-Only Control Group
T1T1 T2T2 T3T3
OO XX OO
OO
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““SOLOMON” FOUR - GROUP SOLOMON” FOUR - GROUP DESIGNDESIGN
T1T1 T2T2 T3T3
OO XX OO
OO OO
XX OO
OO
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More Complex Experimental More Complex Experimental DesignsDesigns
Completely randomized designsCompletely randomized designs
Randomized block designRandomized block design
Factorial designFactorial design
Latin square designLatin square design
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Experimental ConditionsExperimental Conditions
Double Blind experiment – neither Double Blind experiment – neither “observer” nor the “subjects” know “observer” nor the “subjects” know whether the subject are in the treatment or whether the subject are in the treatment or control groups or receiving a placebo.control groups or receiving a placebo.Placebo effect – One experimental group Placebo effect – One experimental group is given the “treatment” that is being tested is given the “treatment” that is being tested while another “treatment” group receives a while another “treatment” group receives a “treatment” but one that is, by design, “treatment” but one that is, by design, “benign” in its effect.“benign” in its effect.
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Extraneous VariablesExtraneous Variables
HistoryHistoryMaturationMaturationTestingTestingInstrumentationInstrumentationSelectionSelectionMortalityMortality
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Extraneous VariablesExtraneous Variables
History – specific events in the environment History – specific events in the environment between the before and after measurement that between the before and after measurement that are beyond the experimenter’s control are beyond the experimenter’s control
e.g. a major employer closes its plant in a e.g. a major employer closes its plant in a test market areatest market area
Maturation – subjects change during the course Maturation – subjects change during the course of the experimentof the experiment
e.g. subjects become tirede.g. subjects become tired
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Extraneous variablesExtraneous variables (cont -2)(cont -2)
Testing – the before measurement alerts Testing – the before measurement alerts subject to the nature of the experimentsubject to the nature of the experiment– e.g. questionnaire about traditional role of e.g. questionnaire about traditional role of
women triggers enhanced awareness of women triggers enhanced awareness of women in the experimentwomen in the experiment
Instrumentation – changes in measuring Instrumentation – changes in measuring instrument result in response biasinstrument result in response bias– e.g. new questions about women are e.g. new questions about women are
interpreted differently than earlier questionsinterpreted differently than earlier questions
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Extraneous variablesExtraneous variables (cont -3)(cont -3)
Selection – sample selection error occurs Selection – sample selection error occurs because of differential selection of comparison because of differential selection of comparison groupsgroups– e.g. control and experimental groups are assigned e.g. control and experimental groups are assigned
self-selecting groups based on preference for soft self-selecting groups based on preference for soft drinksdrinks
Mortality – sample attrition, some subjects Mortality – sample attrition, some subjects withdraw from experimentwithdraw from experiment– e.g. subjects in one group of students withdraw from e.g. subjects in one group of students withdraw from
schoolschool
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Control for Extraneous VariationControl for Extraneous Variation
Eliminate Extraneous VariablesEliminate Extraneous Variables
Hold Conditions ConstantHold Conditions Constant
RandomizationRandomization
Matching SubjectsMatching Subjects
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Demand CharacteristicsDemand Characteristics
Design procedures that “hint” to subjects Design procedures that “hint” to subjects about the experimenter’s hypothesisabout the experimenter’s hypothesis– Guinea Pig effect – when subjects exhibit Guinea Pig effect – when subjects exhibit
behavior that they feel is expected of thembehavior that they feel is expected of them– Hawthorne effect – causes people to perform Hawthorne effect – causes people to perform
differently just because they know they are differently just because they know they are experimental subjectsexperimental subjects
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Problems of Internal ValidityProblems of Internal ValidityDesignDesign HistoryHistory MaturationMaturation TestingTesting InstrumentationInstrumentation SelectionSelection MortalityMortality
One shot designOne shot design 00 00 NRNR NRNR 00 00
One group One group pre/post test pre/post test designdesign
00 00 00 00 00 00
Static group Static group designdesign XX ?? XX XX 00 00
PosttestPosttestControl Group Control Group onlyonly XX XX XX XX XX XX
Pre/PostPre/PostControl Group Control Group designdesign
XX XX XX XX XX XX
Solomon Four Solomon Four Group designGroup design
XX XX XX XX XX XX
0 = weakness X = factor controlled ? = possible concern NR = not relevant0 = weakness X = factor controlled ? = possible concern NR = not relevant
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Ethical IssuesEthical Issues
HarmHarm““Unfair benefit”Unfair benefit”PrivacyPrivacyConfidentialityConfidentialityDeceptionDeceptionNot using debriefingNot using debriefing