30 – Standard Deviation




Variability refers to the spread of the scores within a distribution. Along with the central tendency, it helps in understanding the data set as a whole. There are four major measures of variability:

    1. Range

    • Difference between the highest and lowest scores [+1]

    2. Interquartile Range

    • Difference between the 75th and 25th Percentile

    3. Variance

    • The degree of spread within the distribution (the larger the spread, the larger the variance)

    4. Standard Deviation

    • A measure of how the average score deviates or spreads away from the mean (defined as the square root of the variance)