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Objective Measurement of Subjective Phenomena

4. Nature of the Construct

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:

Dimension 1: Form of individual differences to be exhibited

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).

Continuous distribution:

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.

Example 3

Continuous behavioral outcome examples:

  1. Intelligence - As assessed using an individually administered intelligence test and indexed by the intelligence quotient (IQ). IQs are usually normed to have a mean of 100 and SD of 15 in the population, and IQs are reported as whole numbers.
  2. Extraversion - Which is often assessed using 10 to 20 items, each answered on a 1-to-5 or 1-to-7 scale. Summing across items results in scale scores, with higher scores indicating higher levels of extraversion.

Dichotomous Distribution:

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.

Example 4

Dichotomous behavioral outcome examples:
  1. Clinical depression - Here, one would decide whether a person meets diagnostic criteria of clinical depression by exhibiting a sufficient number of signs or symptoms of depression.
  2. Mental retardation - A person must meet three criteria – low intelligence, deficits in adaptive behavior, and appearance of these criteria prior to the age of 18 years – to be diagnosed with mental retardation (which is now called intellectual disability).

Polytomous Distribution:

A polytomous distribution is another version of categorical measurement whereby individuals are sorted into more than two mutually exclusive and exhaustive categories.

Example 5

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 ADHD
2 = ADHD, attention deficit alone
3 = ADHD, hyperactivity alone
4 = ADHD, combined attention deficit and hyperactivity

Ordered Categorical Scale:

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.

Example 6

Ordered categorical scale example:

Questions on many self-report inventories ask respondents to indicate their response to each item on a 1-to-5 scale, ranging from 1 = strongly disagree to 5 = strongly agree. Without a substantial amount of work, it is difficult to justify the assertion that the difference between scores of 1 and 2 is equal to the difference between scores of 3 and 4.
Waller, N. G., & Meehl, P. E. (1998). Multivariate taxometric procedures: Distinguishing types from continua. Thousand Oaks, CA: Sage.