For example First list the values in order: 3 4 5 7 9 10 18 (a) As there are 7 values, the median will be the 7 1 2 4 + = th value. Median = 7. (b) The lower quartile will be the 7 1 4 2 + = nd value. Lower quartile = 4. The upper quartile will be the 37 1 4 6 ( ) + = th value. Upper quartile = 10. The interquartile range = upper quartile – lower quartile = 10 4 − = 6 The semi-interquartile range = interquartile range 2 = 6 2 = 3