2. In the last question, we did not account for PPCS respondents' demographic characteristics. We can ask the same question - whether stop duration varies across day and night - and this time narrow the sample down by gender and race to create a subsample of white males. This strategy removes any potentially confounding effects of gender and race, and allows us to isolate the effects of the day/night variable. Below is output from SPSS examining this relationship, use it to answer the following questions: Paired Sample T-test Comparison Mean Std. Dev. t df Sig. Duration of Minutes During Day vs. Duration of Minutes during Night 3.985 18.882 1.701 64 0.094