ABSTRACT

If we take a large sample of men or women, measure their heights and plot them on a frequency distribution, the distribution will almost certainly obtain a symmetrical bell-shaped pattern. This is known as the normal distribution. The least frequently recorded heights lie at the two extremes of the curve. In practice, many biological measurements follow this pattern, making it possible to use the normal distribution to describe many features of a population. It must be emphasised that some measurements do not follow the symmetrical shape of the normal distribution, and can be positively skewed or negatively skewed. The distribution will therefore not fit the symmetrical pattern of the normal distribution. We can tell whether the skew is positive or negative by looking at the shape of the plotted data. The normal distribution is useful in a number of applications, including confidence intervals and hypothesis testing.