The Relation of Test Score to the Trait Underlying the Test

IN 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 &dquo;equal.&dquo; If we administer two tests of the same trait or ability, the two tests having different distributions of item &dquo;difficulty,&dquo; 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, for