lab3 - Psychology 321(SP08 Lab#3 Content A Overview of...

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1 Psychology 321 (SP08) – Lab #3 Content: A. Overview of Dependent Samples t -test B. Computing Dependent Samples t-test using SPSS C. Eeany-Meeny-Miny-Mo A. Overview of Dependent Samples t -test This week in class you (hopefully) learned something about the independent samples t-test. One of the assumptions of this test is that the two groups are independent of each other. Contemplating this assumption invariably led you to the question, while discussing stats over dinner, “Yeah, but what do you do if you know the samples are related, like before and after tests on the same people or husband/wife pairs rating their marital happiness??” The answer you are seeking has been in your book all along (Chp. 13, btw); the dependent samples t-test!! This is a wily test that has many aliases, including related-samples, matched-samples and paired-samples t-test. Don’t be fooled…it’s all the same thing. The basic idea behind this test is to get rid of the dependence between the two scores. That is done by finding a difference scores between the two measurements (i.e. posttest – pretest). By doing this, you are also able to remove some individual differences (which is a very good thing). Once you have the difference scores, you just do a one-sample t-test with them. Just to make you memorize something else, there is a specialized formula: t = M diff – 0 with df = N – 1 where N = # of difference scores (s D / N) but notice that it isn’t actually different from the one-sample t-test you already know and love t = M sample – M pop . with df = N – 1 where N = # of scores (s sample / √ N)

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lab3 - Psychology 321(SP08 Lab#3 Content A Overview of...

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