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Lecture 8

FRHD 3070 Lecture 8: Week 8 – Experimental Designs
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by OneClass845058 , Fall 2017
6 Pages
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Department
Family Relations and Human Development
Course Code
FRHD 3070
Professor
Hendry
Lecture
8

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1. Week 8 – Experimental Designs
Overview of Research Designs
-Descriptive – Non-experimental
oObservational Method
oCase Study method
oSurvey method
-Predictive – non-experimental
oCorrelational method
oQuasi-experimental method
-Explanatory – experimental
oExperimental method
True Experiments
-Posttest – only design
-Pretest-posttest design
-Random assignment to conditions
-Experimental control of all other variables
oGiven the above, any difference on the dependent variable should be due to the
effect of the independent variable
oShould try and reduce noise as much as possible
Experimental Designs
-A pre-test helps ensure that groups are equivalent before the IV was introduced
-With large enough groups, randomization usually ensures that groups are equivalent
-The larger the sample, the less likely it is that the groups will differ in any systematic
way
-General rude is that you will probably need a minimum of 30 participants per condition
to ensure no selection differences exist
-Pretest might be necessary when:
oSmall sample size
oPre-test might be necessary to select the participants
E.g. Lowest or highest alcohol consumption, once identified, then
assigned randomly to experimental and control conditions
oMight want to measure the extend of the change in each individual
oPotential for drop out
Called mortality – has the potential to effect equivalence over the course
of the experiment
oMortality might be related to IV or might be unrelated
Example – treatment program designed to reduce smoking. What if the
heaviest smokers in the experimental condition leave the program?
oPre-test enables us to assess the effects of mortality
-Disadvantages of pre-tests?
oTime consuming
oCan sensitize participants to the research questions which might influence their
responses
oIf detection of the pre-test poses a problem, can conduct Solomon four-group
design. This disguises the pre-test by employing a combination of both post-test
only and the pre-test post-test design
-Solomon four group design
-If there is no impact of the pre-test, the post-test scores will be the same in the two
control groups and in the two experimental groups
Between Participants Designs
-Thus, far we have discussed simple experimental structures that are considered
Intendent Groups designs (also called Between Participants designs)
oDifferent participants are assigned to each of the conditions using random
assignment
oIn the Between Participants design random assignment will prevent any
systematic biases and the groups will be similar in terms of participant
characteristics (e.g. Income, age, intelligence, political attitudes)
-Defined
oParticipants in a study are exposed to only one level of the independent variable

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Description
1. Week 8 Experimental Designs Overview of Research Designs Descriptive Nonexperimental o Observational Method o Case Study method o Survey method Predictive nonexperimental o Correlational method o Quasiexperimental method Explanatory experimental o Experimental method True Experiments Posttest only design Pretestposttest design Random assignment to conditions Experimental control of all other variables o Given the above, any difference on the dependent variable should be due to the effect of the independent variable o Should try and reduce noise as much as possible Experimental Designs A pretest helps ensure that groups are equivalent before the IV was introduced With large enough groups, randomization usually ensures that groups are equivalent The larger the sample, the less likely it is that the groups will differ in any systematic way General rude is that you will probably need a minimum of 30 participants per condition to ensure no selection differences exist Pretest might be necessary when: o Small sample size
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