Measures of Variability Variability is how much the numbers(scores) vary in your research. There are four measures of variability: Range: The Range is a the measure of variability from the highest score to the lowest score. for example, if your points are {1, 10, 30, 50, 65, 90} the range would be 89 because you take the highest number, 90, minus the lowest number 1, and that equals 89. Interquartile range: To find this measure of variability, your need to know what the 25th, 50th and 75th percentiles are. The 25% percentil is the line where it cuts off the lower 25% percent of the graph. The 50th percentile where "it cuts the graph in half" The 75th percentile is the line that cuts of the highest 25%. Now that we know what percentiles are, we can understand what the interquartile range is. The interquartile range is the range between the 25th and 75th percentile for example, if the 25th percentile was 30, and the 75 percentile is 90, then the interquartile range would be 60. Variance: Variance is simply how far away is a point from the mean. For example if the mean is 5, then a score of 2 the variance would be 3. Standard Deviation: Standard Deviation is the variance squared. Taking the variance from the example 2, you would take the variance and square it. 2^2 = 2. You can use standard deviation for comparing other experiments. APA sources: Lane, David. (2003). Measures of Variability. Retrieved November 7, 2008 at http://cnx.org/content/m10947/latest/. All Psych Online. (2004). Research Methods. Retrieved Novermber 7, 2008 at http://allpsych.com/researchmethods/variability.html.