ABSTRACT
The terms variability, spread, and dispersion are synonymous, and refer to how spread out a distribution of scores is. Although measures of central tendency focus on how scores in a distribution are congregated around the middle of the distribution, measures of variability are concerned with how the scores are spread out or dispersed along the distribution. In the social sciences, variability serves two major goals. First, many of the statistical inferential tests employed for testing hypotheses require knowledge of the variability of the scores. The range is the easiest measure of variability to calculate, and is defined as the difference between the highest score and the lowest score in a distribution. The standard deviation is simply the average deviation score about the mean of a set of scores. By this definition, the calculation of the standard (average) deviation follows the same logic as calculating the average or mean of a set of raw scores.
