Interquartile Range Ð 25th, 50th, 75th, 90th,
etc 25th quartile Ð 25% of all scores fall below this score
75th quartile Ð 75% of all scores fall below
Semi-interquartile Ð Q3ÐQ1 (middle 50%) Ð not affected by
These are CRUDE MEASURES OF VARIABILITY - does
not tell the whole story about the raw data. A mean of 5.3 does not tell if
most of the scores were similar. So, we have measures of variability, which
tell us about the spread of the scores on the scale of measurement.