The most common of the psychoactive substances, used by ________ % of Americans, is caffeine.

Michelle and Deana are arguing about the relative benefits of breastfeeding and bottle feeding. Which of their arguments is most valid?

a. Michelle's claim that breastfed babies are ill less often because breast milk has the mother's antibodies in it. b. Deana's assertion that bottlefed babies are less likely to have diarrhea and constipation. c. Michelle's argument that breastfed babies' psychological development is enhanced. d. Deana's belief that bottlefed babies make the transition to solid foods more easily.

If Mohammed took the same achievement test at three different times and received scores of 100, 55, and 75, the test would have low levels of

a. validity. c. sampling behavior. b. representativeness. d. reliability.