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Chapter 8

Chapter 8.docx

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Connie Boudens

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Chapter 8 CONFOUNDING AND INTERNAL VALIDITY  A confounding variable: a variable that varies along with the independent variable and there is a confusion about whether the confounding variable or the independent variable caused the results  Internal validity: when the results of an experiment can confidently be attributed to the manipulation of the independent variable BASIC EXPERIMENTS  Has an independent variable and a dependent variable  The independent variable has at least 2 level experimental group and control group  The only difference between the 2 levels should be the manipulated variable POSTTEST ONLY DESIGN  Obtain 2 equivalent groups of participants (experimental and control)  Introduce the independent variable  Measure the effect of the independent variable on the dependent variable  The participants can either be randomly assigned or have them participate in both the conditions  Another approach would be to use 2 different amounts of the independent variable  Another approach would be to use 2 qualitatively different conditions  Has a high degree of internal validity PRETEST-POSTTEST DESIGN  A pre test is given that ensures that the levels only varies in terms of the manipulated variable  The larger the group, the less likely it is that the groups will differ systematically  If the group is small, a pre test helps ensures that the groups don’t vary systematically  Sometimes it is necessary to select participants for the 2 groups  A pre test is also necessary when there is possibility that participants will drop out Attrition o The smoking experiment example; heavy smokers drop out  A pre-test can be time consuming  It can sensitize the participants and they may react differently  A solution to that would be disguising the pre test in a completely different situation and embedding the pre test in a set of completely irrelevant measures  SOLOMON FOUR GROUP DESIGN o Half the participants receive only the post-test and half of them receive the pre-test post-test o If there is no effect of the pre-test, the post-test scores will be the same in the 2 control and experimental groups. ASSIGNING PARTICIPANTS TO EXPERIMENTAL CONDITIONS INDEPENDENT GROUPS DESIGN/ BETWEEN-SUB
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