||The term “reliability” refers to the degree to which a measurement procedure is free from unsystematic errors of measurement and the degree to which it gives the same values if the measurement procedure is repeated. An individual responding to a measure is likely to have slightly different results if he or she took the instrument again. If these differences are the result of unsystematic errors, the instrument is said to have low reliability. The higher the reliability of a measure, the more confidence you can have in the information obtained from the measure.
There are several ways to assess the reliability of measurement, depending on the type of consistency with which one is most concerned, including internal consistency and test-retest reliability. The following subsections will highlight the evidence gathered on the Career Personality Test that related to each of these two types of reliability.
Internal Consistency. This type of reliability is used to determine whether different questions, which are measuring the same subject on the same scale, have highly related results. For example, if a test included 10 items on math ability and 10 items on reading ability, one would expect to see higher interrelationships within the set of 10 math ability items and within the set of 10 reading ability items than between items from the two different sets. Thus, internal consistency reliability is important for the Career Personality Test because one would expect high internal consistency among the questions that comprised each of the four scales.
The instrument did, in fact, exhibit very high internal consistency estimates across all four scales (coefficient alphas ranging from .86 to .95), indicating that each of the scales “hangs together” well. Thus, it could be said that on the basis on internal consistency the instrument has very high reliability.
Test-Retest Reliability. This type of reliability refers to the consistency of results when the same individual is administered on the same test at two points in time. This information is obtained by looking at the degree of relationship (i.e., correlation) between an examinee’s two scores. Estimates of test-retest reliability are particularly useful if the characteristic being measured is not expected to change over time between the two measurement periods. Given that the personality characteristics are considered to be relatively stable characteristics, one would expect that the participants’ responses would be very stable across a short period of time.
The instrument did, in fact, exhibit very high test-retest reliability (ranging from .81 to .92), providing evidence that clients’ scores are likely to be similar if the instrument is taken more than once within a short period of time.