Categorical data: two proportions
The Problems We have two independent groups of individuals (e.g. homosexual men with and without a history of gonorrhoea). We want to know whether the proportions of individuals with a…
Numerical data: two unrelated groups
The Problem We have samples from two independent (unrelated) groups of individuals and one numerical or ordinal variable of interest. We are interested in whether the mean or distribution of…
Performing a linear regression analysis
The Linear Regression Line After selecting a sample of size n from our population and drawing a scatter diagram to confirm that the data approximate a straight line, we estimate…
Binary outcomes and logistic regression
Introduction Logistic regression is very similar to linear regression; we use it when we have a binary outcome of interest (e.g. the presence/absence of a symptom, or an individual who…
Diagnostic tools
An individual’s state of health is often characterized by a number of numerical or categorical measures. In this context, an appropriate reference interval (Chapters 6 and 7) and/or diagnostic test…
Sample size calculations
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…
Numerical data: two related groups
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…
Checking assumptions
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’…
Numerical data: more than two groups
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…
Bayesian methods
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…
