The most frequently abused illicit drug in the United States is

In general, stress

a. decreases with age for females, but increases with age for males. b. stays about the same over the life span. c. increases with age. d. decreases with age.

The standard error of the mean of difference scores could be calculated by

a. taking the standard deviation of the differences. b. repeating the study many times and looking at the distribution of means. c. dividing the standard deviation of difference scores by the square root of the sample size. d. looking at the standard deviation of the posttest scores.