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Hypothesis Tests with Related Samples

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Presentation on theme: "Hypothesis Tests with Related Samples"— Presentation transcript:

1 Hypothesis Tests with Related Samples

2 Difference scores Calculate difference between first and second score
e. g. Difference = After (X2) – Before (X1) OR X1 – X2 Base subsequent analysis on difference scores

3 Example Industrial psychologist is concerned that a recent round of layoffs at a plant may have increased the stress felt by employees who retained their positions Hypothesis: Employees will report more stress after layoffs occurred

4 Participant n = 7 XBEFORE XAFTER 1 21 23 2 24 26 3 15 4 18 22 5 19 20 6 7

5 The question to answer: Is the mean difference significantly different from what we would expect it to be if Ho was true (i.e., 0)? t = MD - μD sMD

6 Sums of squares:

7 Effect size

8 Effect size r2 = Percentage of variance accounted for by the effect
r2= t2 t2 + df

9 Assumptions 1. Observations within each treatment condition must be independent 2. Population of difference scores must be normally distributed


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