Personal characteristics differ in the nature of individual differences that are presumed to exist. As a result, the researcher must outline the nature of the personal characteristic to be measured. When measuring a characteristic, one might consider the following dimensions:
Individual differences on an attribute of interest may be quantitative or may be qualitative. Quantitative differences are typically seen indexing “more vs. less” of an attribute along a continuous scale, whereas qualitative differences usually take the form of identifying either a group of which the person is a member or a distinct characteristic that a person possesses (or does not possess) (Waller & Meehl, 1998; Widiger & Trull, 2007).
A continuous distribution is a very common conception, in which individual differences are represented by numbers on a scale that indicates a person has more (or less) of the characteristic.
Continuous behavioral outcome examples:
One version of a categorical scale, a dichotomous distribution indicates whether a person falls in one or the other of two mutually exclusive and exhaustive classes or groups. Thus, a dichotomous distribution involves making a binary choice of group membership for each person.
A polytomous distribution is another version of categorical measurement whereby individuals are sorted into more than two mutually exclusive and exhaustive categories.
Polytomous behavioral outcome example:
Attention Deficit/Hyperactivity Disorder (ADHD). ADHD is often identified using one set of symptoms for attention deficits and another set for hyperactivity. Then, a child might fall into one of four groups:
1 = no ADHD2 = ADHD, attention deficit alone3 = ADHD, hyperactivity alone4 = ADHD, combined attention deficit and hyperactivity
An ordered categorical scale is one on which numbers indicate more or less of an attribute, but score intervals are not equal. Thus, scale scores seem similar to those on a continuous scale, but scores on an ordered categorical scale do not fall on an equal-interval scale. Most rating scales used in the social and behavioral sciences are most accurately characterized as falling on ordered categorical scales.
Ordered categorical scale example: