Random assignment of subjects to groups in an experiment is used to reduce the effects of extraneous variables, such as personality

Sleep terrors and sleepwalking generally occur a. during REM sleep

b. during the twilight stages between sleep and waking. c. during NREM sleep. d. after some severe daytime stressor.

A participant's ideas and expectations about an experiment give rise to

a. evaluation apprehension b. role demands c. experimenter bias d. selection bias