ABSTRACT
This chapter describes the concept of standard deviation as how much scores differ from the mean of a group on average. It explains the 68% range in a normal distribution and the higher the standard deviation the higher the variability. The chapter shows that standard deviation is reported along with the mean in a normally distributed data. The standard deviation is the most frequently used measure of variability. Synonyms for variability are spread and dispersion. Variability refers to the differences among scores of participants. The more spread out the participants' scores are around their mean, the larger the standard deviation. The standard deviation is a statistic that provides an overall measurement of how much participants' scores differ from the mean score of their group on average. It is a special type of average of the deviations of the scores from their mean.
