Normal Probability Distribution

Psychological tests are often standardized. This means the administration is consistent, and test administrators can use published norms to score the results (i.e., an individual’s results can be compared to the normative data, which represents the population as a whole, and that individual’s scores can be summarized and reported in terms of how they compare to the population from which the normative data was collected).

An example often used in psychology textbooks is the Wechsler Adult Intelligence Scale (WAIS), often referred to as an IQ test. The WAIS has a normative mean of 100 and a standard deviation of 15 points. Any person’s score on the WAIS can be summarized in various ways, for example, as the distance from the mean, or in terms of quartiles or percentiles.

Use the Assessment Psychology Online website, or conduct an Internet search to identify another behaviorally oriented standardized test (i.e., not the WAIS), and respond to the following:

1. Start with a general description of the instrument, including who developed it, its intended purpose, and how it is administered.
2. Describe the normative data (i.e., the mean, standard deviation, and any other relevant parameters).
3. What would be the probability of a person chosen at random from the population scoring more than 1.0 standard deviation above or below the mean?
4. Describe, in behavioral terms, what a z-score of 1.0 represents.