Jaymie Ticknor Quantitative Methods 2317 Sect 001 7 and 17 March 2014 Lecture 8 Chapter 8 T test for Independent Means Used when you want to compare two sets of scores each from separate groups of people Comparison distribution is a distribution of the differences between means If null hypothesis is true there will be no difference in means between the groups difference in means will be zero goal is to find out given our sample how unlikely likely this is then decide whether to reject or fail to reject the null hypothesis If research hypothesis is true the mean of one sample is so far from the mean of the other sample that we can conclude the two means not only came from separate samples but separate populations Formulas S2 X M 2 N 1 1 df2 dftotal S2 2 Pooled df1 dftotal S2 S2 M1 S2 S2 Pooled N1 M2 S2 S2 Pooled N2 S2 Difference S2 SDifference S2 dftotal df1 df2 t M1 M2 SDifference Cohen s d M1 M2 SPooled M1 S2 Difference M2 Sampling comparison distribution is normally distributed two populations have the same variance homogeneity of variance
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