There are three measures to central tendency: the mean, median, and mode. These measures relate in different ways to different distributions either skewed or normal. Intelligence tests can also be measured using central tendency principles as well each has a distribution. Intelligence tests also are biased in material, and need regular updates.
The mean is the average score, or the sum of the scores divided by the number of different scores. The median is the middle number in a set, which divides a distribution in half. The mode is the most frequent score, which shows up the most often. A distribution is the curve of scores. A skewed distribution is a curve that has a long tail in one direction and has extreme scores that change the mean. The three measures mean, median, and mode under a normal distribution are all the same. Also, in a positively skewed distribution the mean is the greatest number, as to the median and mode. An intelligence test measures the abilities of a person and distributes it as a score. Under the standard, most scores are within 15 points of the mean, being 85 and 115. In two normal distributions there can be an overlap as some people score above and below the mean between the groups. To determine if a test is biased then the scores of two groups need to be measured to see if the test is biased or not.