Psychology Select THREE facts about standard deviations.

They are inferential statistical tools.
They are the most widely used measures of variability.
They are computed by dividing the mean by the number of scores.
Psychologists only use them when statistical reliability is greater than 99%.
They are arbitrary computations that create simple numbers representing how close a score is to the mean.
Standard deviations less than –3 or greater than 3 are unusual because they represent less than 1% of all scores.