Psychological Testing

You are familiar with devices used to measure physical characteristics: the bathroom scale to measure your body weight, the ruler to measure length or distance. But what about psychological characteristics such as introversion/extroversion, aptitude, or intelligence? For those characteristics, too, there are special devices used to measure them, called psychological tests. In fact, these are real measuring instruments, and are sometimes actually referred to as instruments.

To be of any value, psychological tests must have certain properties. In this paper I describe those characteristics and how we go about assessing them. After that, I review a selected sample of psychological tests.

Properties of a Good Psychological Test

Three important properties of any good psychological test are validity, reliability, and (where appropriate) standardization. Below I define each of these properties and describe ways in which those properties are established.

Validity

A psychological test is said to be valid if it measures what it is intended to measure. An intelligence test, for example, is valid to the extent that it does measure intelligence and not simply some other variable, such as knowledge. A number of ways to assess the validity of a test have been developed; here I will describe a few of them.

Reliability

A psychological test is reliable to the extent that it produces similar results when the individual is repeatedly tested under the same conditions. There are two main methods used to assess reliability, described below.

Standardization

In tests of physical characteristics such as weight, it is possible to establish the accuracy of the measurement by comparing measurements against a set of known standards. For example, a scale could be checked against standard weights of 50 grams, 100 grams, 500 grams, and so on. If inaccuracies were found, the scale would be calibrated to remove them. Standard samples for many variables are available from the National Bureau of Standards.

For psychological characteristics, there are no standard samples that one can purchase and use to evaluate the accuracy of the test. (For example, you cannot rent a person known to have an I.Q. of exactly 100.) Thus, to standardize psychological tests, a different method is needed. What is actually done is to administer the test to a large sample of individuals from the population for which the test is intended, and then compute certain group statistics, usually the mean and standard deviation. These provide the average value across individuals and the amount of variability, and are used to determine a formula for converting raw scores to standard scores. For example, different I.Q. tests are standardized so that the average I.Q. on the test is 100.

Some Examples of Psychological Tests

Psychological tests abound; here I provide only a few major categories and examples.