16. Statistics in Psychology

The simplest, quickest, but also crudest method for finding the amount of variability in a set of scores is to compute the:

Why are measures of variability used when describing a set of scores?

Dr. Recitative eyeballed a large set of scores: 170, 170, 168, 168, 168, 167, 166, 166, 165, 164, 164, 164, 164, 164, 163, 160, 159, 159, 158 ,157, 157, 157, 156, 155, 155, 155, 155, 155, 152, 152, 150, 149, 148, 148, 148, 147, 147, 146, 145, 145, 145, 145, 143, 140, 140, 140, 140. 'Okay, so the range here is 30,' she announced, then moved on to scan another set of responses. Edgar, her lab assistant, whispered to Yulya, 'How did she do that so fast, eh?!' Yulya replied:

Arnie was trying to memorize a formula for his upcoming quiz in Statistics. 'Score minus the mean, square it; next score minus the mean, square it; next score minus the mean, square it; do that for all the scores, add up all those squared differences, and divide the total by N, the sample size; then take the square root of the whole mess. Got it!' And indeed he does! Arnie has memorized the formula for computing:

A distribution of scores has a mean of 50 and a standard deviation of 10. This indicates that a score of _________ falls one standard deviation below the mean, and a score of ___________ falls one standard deviation above the mean.