Measures of Variability

Variability

An indication of how scores in a distribution are scattered or dispersed

Measures of Variability

Statistic that describe the amount of variation in a distribution

Range

Equal to the difference between the highest and the lowest score

Range

The simplest measure of variability to calculate but its potential use is limited

Range

Provides a quick but gross description of the spread of scores

Interquartile Range

A measure of variability equal to the difference between Q₃ and Q₁

Semi-interquartile Range

Equal to the interquartile range divided by 2

Interquartile and Semi-interquartile Ranges

A distribution of test scores can be divided into four parts such that 25% of the test scores occur in each quarter

Quarter

Refers to an interval

Quartiles

The dividing points between the four quarters in the distribution

Quartiles

Refers to a specific point