Assessment, Statistics, and Research

  The concept of average intelligence is sometimes difficult to appreciate because the two words, average and intelligence, are sometimes not defined. Average   To psychologists and counselors who administer tests of intelligence, a person who scores at the 50th Percentile has average intelligence as defined by the number of correct answers to test tasks compared to others in their age group. Many tests set the middle score at 100 thus, 100 = average intelligence on many tests. All test scores vary from time to time so, a person may earn more or less points on another day. This fluctuation is estimated and can range for example by plus or minus 3-5 IQ points depending on the test and age group.  If you retake the test in a month or so, you may score better because of the “practice effect”—you’ve seen the items recently so you will probably do better. There is an average range so examiners will not focus on the obtained score but consider a broader range. For example, some...

In testing, measurement error usually refers to the fact that the same people can obtain different scores on the same test at different times. In a broad sense, measurement error can also refer to the degree of accuracy of a test to correctly identify a condition, which is discussed as test validity. Recall that test score reliability is a necessary but insufficient condition for test score validity. Many tests in psychology, medicine, and education are useful. The reliability of the scores will vary depending on such factors as the properties of the test itself as well as how well the user follows standard procedures in administering the test, environmental factors that can affect the scores, and factors within the person taking the test. The scores on many tests conform to the pattern called the normal curve or bell curve. In classical test theory, the scores people obtain on tests are simply called obtained scores (symbol X). Statisticians consider the variation in scores t...