![]() ![]() In the above example, the upper quartile is the 118.5th value and the lower quartile is the 39.5th value. The difference between these two is the interquartile range (IQR). 157 in this case) and the upper quartile is the 3(n+1)/4 the value. ![]() The lower quartile is (n+1)/4 th value (n is the cumulative frequency, i.e. The interquartile range is a method of measuring the spread of the middle 50% of the values and is useful since it ignore the extreme values. However, the extremes in this set (8 and 50) distort this value. If we divide a cumulative frequency curve into quarters, the value at the lower quarter is referred to as the lower quartile, the value at the middle gives the median and the value at the upper quarter is the upper quartile.Ī set of numbers may be as follows: 8, 14, 15, 16, 17, 18, 19, 50. The corresponding 'x' value is an estimation of the median. To find this, on the cumulative frequency curve, find 13 on the y-axis (which should be labelled cumulative frequency). Therefore the median would be the 13th value. When dealing with a cumulative frequency curve, "n" is the cumulative frequency (25 in the above example). For example, there are 7 numbers in the example above, so replace n by 7 and the median is the (7 + 1)/2 th value = 4th value. If you have n numbers in a group, the median is the (n + 1)/2 th value. For example, if the set of numbers is 4, 1, 6, 2, 6, 7, 8, the median is 6:ġ, 2, 4, 6, 6, 7, 8 (6 is the middle value when the numbers are in order) The median of a group of numbers is the number in the middle, when the numbers are in order of magnitude.
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