ABSTRACT
This chapter introduces the principles and methods of epidemiology: the basic science for studies of the distribution and determinants of any characteristic in a population. It discusses the historical origins of the subject in studies of diseases and of public health, and the many similarities between such work and studies of crime in populations. It introduces the several possible approaches (observational versus intervention, descriptive versus analytic) and designs (surveillance, cross-sectional, ecological, longitudinal, cohort, case-control, individual and cluster randomised trials) and the inferences which can be drawn from them, as well as the basic measures of incidence, prevalence, risks, odds, risk ratios and odds ratios by which we describe the patterns and determinants of diseases, crimes, or other features of populations. The basic concept of risk is emphasised (the probability of some event occurring in a particular place or group over a particular time), along with a discussion of risk factor (the various characteristics associated with high or low risk), as well as the problems of distinguishing causal relationships from those which are just coincidental or due to confounding because of the complex relationships between the various individual and social characteristics and behaviours in society. The importance of data quality in all research is stressed, along with the concepts of sensitivity, specificity, repeatability and validity of various measures either collected or derived. Finally, the problem of assessing the effectiveness of interventions is discussed, applying concepts of efficacy, effectiveness and impact. The chapter emphasises analogies between the approaches and methods used in all the population sciences, and the importance of communication between them.
