10. Comparing Two Population Means

# 10.10 SPSS Lesson 7: Paired Sample t-Test

As set up, the file has two dependent variables. This “within subjects” dataset is fundamentally multivariate. When we did the paired -test by hand we converted the multivariate data to univariate data by taking differences. SPSS will do the differences behind the scene and you won’t actually see them. Run the -test by picking Analyze Compare Means Paired -Samples T-Test:

Move the two variables into Pair 1 and hit OK (Options again allows you to specify a confidence intervals percentage):

The output is:

The first two tables are descriptive statistics. The last table gives the stuff we want: , , the confidence interval

(10.11)  , and for the two-tailed hypotheses pair (10.12) The very low -value (0 in this case) and the absence of 0 in the confidence interval guide us to reject , the differences are significantly different from zero.

The standardized effect size and strength of association for the paired -test are

(10.13) and

(10.14) respectively. 