How closely related are results on short cognitive skills tests and a grade point average over several years in college? In Data D.1 on page 599, we introduce the data in SleepStudy. Two of the variables in that study are Cognition Z score, which is a standardized z-score derived from multiple tests of cognitive skills such as recalling a list of words, and GPA, grade point average on a 4-point scale. The sample correlation between these two variables is r = 0.267 with n = 253. Test to see if there is evidence to show a positive association between these two variables in the population.

Data D.1 on page 599

A recent study examines the relationship between class start times, sleep, circadian preference, alcohol use, academic performance, and other variables in college students. The data were obtained from a sample of students who did skills tests to measure cognitive function, completed a survey that asked many questions about attitudes and habits, and kept a sleep diary to record time and quality of sleep over a two-week period. Some data from this study are available in SleepStudy.