Читать книгу Medical Statistics - David Machin - Страница 70

If the n observations in a sample are arranged in increasing or decreasing order, the median is the middle value. If there are n observations the median is the ½(n + 1)th ordered value. If the number of observations, n, is odd there will be a unique median – the ½(n + 1)th ordered value. If n is even, there is strictly no middle observation, but the median is defined by convention as the mean of the two middle observations – the ½nth and (½n + 1)th.

Calculating the median for the foot corn size data, as the number of observations is even (n = 16), the median is the average of the two middle observations – the ½(16)th and ([½ × 16] + 1)th, i.e. the eighth and ninth ordered values. So the median corn size is (3 + 3)/2 = 3 mm.