PSYC227_fall09_2sample_t

# PSYC227_fall09_2sample_t - LearningObjec-ves -...

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Learning Objec-ves Describe experimental situa-ons for which independent‐ measures t sta-s-c is appropriate Use the independent‐measures t‐sta-s-c to test hypothesis about the mean difference between two popula-ons Know assump-ons required for the independent‐measures t‐ sta-s-c to be interpretable Learn measures of effect size for the independent‐measures t (r 2 and Cohen’s d) t‐test for 2 Independent Samples

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When the population variance is unknown When the population variance is known Computation: df = n-1
Between‐subjects research design Independent‐measures or between‐subjects design Separate sample for each treatment condi-on ex. men vs. women; students taught by method A vs. method B Repeated measures or within‐subjects design Samples obtained from the same set of data ex. Depression scores before and aMer therapy.

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Two Independent Samples How can we compare responses from two separate groups on a given measure? Suppose subjects are randomly assigned to the two groups (e.g., Experimental vs. Control group). Each group may be a random sample from a specific popula-on (e.g., female / male).

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Sta-ng the hypotheses Study of effects of aging and gender on short term memory in adults. 125 adults were asked to place 20 common objects (e.g. eyeglasses, keys) into the rooms of a computer‐image house. AMer performing some unrelated ac-vi-es, each subject was asked to recall the loca-ons of the objects they had placed. The number of correct responses (out of 20) was recorded. 1. The researchers theorized that women will have a higher mean recall score than men. Set up the hypotheses to test this theory.
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