Читать книгу Medical Statistics - David Machin - Страница 44

A third measure of location is termed the mode. This is the value that occurs most frequently, or, if the data are grouped, the grouping with the highest frequency. It is not used much in statistical analysis, since its value depends on the accuracy with which the data are measured; although it may be useful for categorical data to describe the most frequent category. However, the expression ‘bimodal’ distribution is used to describe a distribution with two peaks in it. This can be caused by mixing two or more populations together. For example, height might appear to have a bimodal distribution if one had men and women in the study population. Some illnesses may raise a biochemical measure, so in a population containing healthy individuals and those who are ill one might expect a bimodal distribution. However, some illnesses are defined by the measure of, say obesity or high blood pressure, and in these cases the distributions are usually unimodal with those above a given value regarded as ill.

Table 2.4 The 16 corn sizes ordered and ranked from smallest to largest.