An introduction to medical statistics for health care professionals: basic statistical tests

This article, the third and final article in the series, aims to give health care professionals (HCPs) a sound and helpful introduction to medical statistics (Thomas, 2004, 2005). A brief summary of the content of the previous articles is given in Table 1. The current article will cover the area of basic statistical tests with the aim of guiding HCPs to the correct test for a particular research question and dataset. The article will not go into great depth of the formal methods of calculation required for all the tests covered but I would suggest that the reader refer to standard textbooks (Jordan et al., 1998; Swinscow, 1998; Altman, 1994; Bland, 2000), the help sections of statistical packages (SPSS or Stata), or consult a statistician. For ease of reference within the article the tests have been grouped by the data type, i.e. numerical or categorical. Further separation within each data type has been carried out depending on the number of groups being compared, whether the groups are independent, the size of the sample, and, in the case of numerical data, the distribution of the variable. For quick reference, two other tables are also presented which summarize which analysis methods should be used in each situation.