Basicmedical Key

Measurement Variability and Error A biological variable measured on each of a number of individuals will always exhibit a certain amount of variability. The measurements are likely to vary between…

Introduction Correlation analysis is concerned with measuring the degree of association between two variables, x and y. Initially, we assume that both x and y are numerical, e.g. height and…

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…

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…

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…

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…

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…

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…

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…

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’…