The Relation of Test Score to the Trait Underlying the Test

Educational Testing ServiceIN any consideration of the nature of the metric provided by the raw score on a mental test, one is likely to be faced with the fact that the raw score units of measurement cannot ordinarily be considered as "equaL" If we administer two tests of the same trait or ability, the two tests having different distributions of item "difficulty," to the same group of examinees, we will obtain two different shapes of raw score distributions from the two tests, as illustrated in Figure I l for >o