The interquartile range

4-1: Understand why measures of variability are calculated in addition to measures of central tendency.

4-2: Calculate and interpret measures of variability (range, interquartile range, variance, standard deviation) for a set of data.

4-3: Understand the difference between the range and the interquartile range.

The variance (s²)

4-4: Understand why calculating the variance involves squaring the deviation of each score from the mean.

4-5: Understand why, in calculating the variance, the sum of squared deviations is divided by N - 1 rather than N.

4-6: Understand the difference between a biased estimate and an unbiased estimate.

The standard deviation (s)

4-7: Understand the relationship between the variance and the standard deviation.

Measures of variability for populations

4-8: Understand the difference between the population standard deviation and the standard deviation.

4-9: Understand when you would calculate the population standard deviation for a set of data rather than the standard deviation.