What percentage of persons over 85 years old report that their visual problems are serious enough to interfere with their daily lives?

A __________ is a very frightening dream that occurs during REM sleep

a) nightmare b) sleep terror c) night terror d) narcoleptic fit

In his study on the relation between optimism and exercise, Huck found a positive correlation that was explained by the observation that having a large social network caused people to be optimistic and to exercise. Therefore, social network size was a(n):

a. confound b. moderator c. third variable d. artifact e. mediator