The Problem We have two samples that are related to each other and one numerical or ordinal variable of interest. The variable may be measured on each individual in two…

The Importance of Sample Size If the number of patients in our study is small, we may have inadequate power (Chapter 18) to detect an important existing effect, and we…

Why Bother? Computer analysis of data offers the opportunity of handling large data sets that might otherwise be beyond our capabilities. However, do not be tempted to ‘have a go’…

The Problem We have samples from a number of independent groups. We have a single numerical or ordinal variable and are interested in whether the average value of the variable…

The Frequentist Approach The hypothesis tests described in this book are based on the frequentist approach to probability (Chapter 7) and inference that considers the number of times an event…

A cohort study takes a group of individuals and usually follows them forward in time, the aim being to study whether exposure to a particular aetiological factor will affect the…

Various regression methods can be used for the analysis of the two-level hierarchical structure described in Chapter 41, in which each cluster (level 2 unit) contains a number of individual…

A case–control study compares the characteristics of a group of patients with a particular disease outcome (the cases) to a group of individuals without a disease outcome (the controls), to…

19 Numerical Data: a Single Group The Problem We have a sample from a single group of individuals and one numerical or ordinal variable of interest. We are interested in…

Chi-Squared Test: Large Contingency Tables The Problem Individuals can be classified by two factors. For example, one factor may represent disease severity (mild, moderate, severe) and the other factor may…