Measures of dispersion describe how similar or spread out scores in a data set are. The three main measures are range, semi-interquartile range (SIR), and variance/standard deviation. Range is the difference between the highest and lowest scores. SIR is less affected by outliers than range. Variance/standard deviation quantify the average squared distance of scores from the mean, with larger numbers indicating more spread out data. Skew and kurtosis further describe the shape of distributions.