Measures of variability

range

biggest value minus smallest value, extremely sensitive to outliers

interquartile range

difference between the 25th and 75th percentile, the range spanned by the middle half of data, one quarter falls bellow the 25th percentile and one quarter falls above the 75th percentile, the IQR covers the middle half

mean absolute deviation

calculate mean of data, then calculate difference between each score and mean (X-mean), convert any negative scores into positive ones, then find the mean of all the deviation scores

variance

calculated same way as mean absolute deviation except squared, uninterpretable in terms of the original variable

standard deviation

the square root of the variance, solves the uninterpretable problem