Epidemiological studies cannot control for selection factors

Butler and Roediger (2007) gave some students a lecture summary whereas other “students” received short answer tests with feedback if the participants for half of the answers. A final control group of participants did not get a summary nor did they receive a short answer test. The group that did the best on a later test was:

a. the control group. b. the group given lecture summaries. c. all groups performed equivalently. d. the group that received short-answer tests.

Which of the following statements holds true of an individual during the different stages of sleep?

A. An individual in Stage 2 experiences no K-complexes. B. An individual in Stage 1 sleep experiences faster sleep spindles than Stage 2. C. An individual in Stage 3 sleep experiences fewer sleep spindles than Stage 2. D. An individual in Stage 3 experiences more K-complexes than Stage 2.