Reliability refers to the attribute of consistency in measurements. However, reliability is seldom an all-or nine matter; more commonly it is a question of degree. Very few measures of physical or psychological characteristics are completely consistent, even from one moment to the next. For example, a person who steps on a scale twice in quick succession might register a weight of 145 pounds the first time and 145 pounds the second. The same individual might take tow presumably equivalent forms of an IQ test and score 114 on one and 119 on the other. Tow successive measures of speed of response-pressing a key quickly whenever the letter X appears on a microcomputer screen-might produce a reaction time of 223 milliseconds on the first and 341 milliseconds on the next. We see in these examples of consistency-the pairs of measurements are not completely random-but different amounts of inconsistency are evident, too In the short run, measures of weight are highly consistent intellect test scores are moderately stable, but simple reaction time is somewhat erratic.