“Percentage error” would be difficult to calculate for IQ tests, because it would require a measurement of the discrepancy between the “exact intelligence” and the measured IQ. Since, there is no way to determine the ”exact intelligence” of a person, calculation of a “percentage error” is not possible.
However, to estimate the “accuracy” of an IQ measurement psychometricians use measures of “reliability” and “validity.” “Reliability” refers to the consistency and stability of test scores, i.e., the likelihood that successive measures of IQ for a person would fall within a particular range. Validity refers to how well the test measures what it is intended to measure, and this involves computing the correlations of IQ test results with other measures of intelligence.
For the WAIS IV IQ test, the reported reliability estimates are usually high, with internal consistency coefficients (Cronbach’s alpha) in the range of 0.87 to 0.98 for most subtests and composites. Essentially Cronbach’s alpha measures the correlations between how individuals perform on each test item with their performance on the entire test.
The validity of IQ tests like WAIS IV has been demonstrated through extensive research, involving correlations with other measures of intelligence, showing it to be a reliable measure of general cognitive abilities in adults. When you receive an IQ score, remember that although it is a very reliable measure on average, it can greatly undervalue an individual’s cognitive skills, depending on a variety of factors such as unfamiliarity with the test formats. Furthermore, IQ tests don’t measure creativity, imagination of the ability to solve difficult problems over a long period of time.
