The square root of the variance is the

a. true variance

A sleep researcher was interviewed on television today. What advice is she most likely to offer adults concerning naps?

a) Naps should be avoided because they negatively impact night-time sleep. b) Naps are often refreshing but shorter naps of around 20 minutes seem best. c) The boost one receives from naps seems real, so nap often and as long as possible. d) Most people experience a feeling called "sleep inertia" following a nap, which is the primary reason for avoiding naps.

Whenever the sampling error is consistently in one direction, the result is

a. a negative sampling error b. a positive sampling error c. a population exclusion d. bias