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Psychology (9,697)
PSYB01H3 (581)
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Chapter 8

Chapter 8 Experimental Design.docx

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Department
Psychology
Course
PSYB01H3
Professor
Anna Nagy
Semester
Summer

Description
Chapter 8 Experimental Design - Variables are kept constant by either experimental control or by randomization - Confounding variable- variable that varies along with the independent variable o Effects of the independent variable and an uncontrollable variable are intertwined so you can't determine which of the variables is responsible for the observed effect - Internal validity- ability to draw conclusions about causal relationships from our data POSTTEST-ONLY DESIGN - 2 equivalent groups of Ps are used o To avoid selection differences- people selected to be in the conditions can't differ in any systematic way o Randomization or having same P do both conditions - Introduce the independent variable o Experimental group gets the treatment o Control group doesn't - Measure the effect of the independent variable on the dependent variable o Same measurement is used for both groups o Statistically significant test can be used PRETEST-POSTTEST DESIGN - In this test, the pretest is given before the experimental manipulation is given - Makes sure that the groups were equal in the beginning of the experiment - Not necessary is Ps were randomized to the groups - Larger the sample, the more equal they will be when randomized - Minimum of 20 to 30 Ps - Pretest may be necessary to select the Ps in the experiment - Focuses on the CHANGE from pretest to post-test - Needed if there's a possibility that the P will drop out (attrition/ mortality) of the experiment - Can be too disadvantage or can sensitize Ps to your experiment - Solomon Four-Group Design- half receive post-test and half receive pretest INDEPENDENT GROUPS DESIGN - Uses random assignment so each P is in only in one group - A.k.a between-subjects design since comparisons are made between different groups of participation REPEATED MEASURES DESIGN - Each P is in every condition - Each P is measure after getting each level of the independent variable - A.k.a within-subjects design - Comparisons are made within the same group of Ps Advantages of Repeated Measures Design - Fewer Ps are needed - Sensitive to finding statistically significant differences between groups - Individual differences can be seen and explained- so greater ability to detect an effect of the independent variable Disadvantages of Repeated Measures Design - Different conditions must be presented in a particular sequence o Order effect- the order of presenting the treatments affects the dependent variable  Ex. greater recall in the high-meaningful condition could be
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