Inferential statistics

In many epidemiological studies, it is not possible to include every individual in a population. Rather, a sample of individuals is collected. This may be take the form of a survey, a cross-sectional study, a randomised controlled trial, and so on. The important issue is that not every individual in the source population is included, which means that random, or sampling, error and biases may be introduced. These affect our ability to extrapolate our results (whether descriptive or analytic in nature) to the source population. However, the aim of most studies is to draw some conclusion about the source population, using the results obtained from the sample. This is known as inferential statistics, and is a very important concept.

Selection biases introduced during sample collection cannot be accounted for in the analysis, and so should either be avoided from the start, or discussed in the analysis report. Statistical methodology employed during analysis of sample data is aimed at accounting for random error in the sample.