Introduction

The recording of mortality and morbidity from communicable diseases has a long history. However, although Pierre Louis described the importance of cancer statistics in the 1830s, the need to measure accurately chronic diseases in humans, such as cancer, was not recognized until the twentieth century.

Definition of epidemiology

Epidemiology, a science based on population measurements, can be described as the study of the distribution and determinants of diseases in human populations and the application of the results to their prevention or control. Unlike the experimentalist who controls risk factors and then observes their effects, the epidemiologist, in general, measures effects and then tries to determine the risk factors. In the traditional observational study, the investigator has no direct control over the assignment of risk factors and must rely on somewhat less efficient methods of design and analysis to uncover associations between the factors and disease endpoints. However, epidemiological methods can also be used to assess the impact of active interventions, introducing the concept of experimentation. The major types of epidemiological studies are:

1. (a) Descriptive: These studies examine differences in the distribution of disease occurrence with respect to population, place and time. These investigations include correlational analysis, case series and case reports. In general, such studies cannot address specific causal hypotheses, but may generate them.

2. […]