Basics of epidemiology; Part III: Statistical association and cause-effect relationship

ABSTRACT

In this; the third part of a series on basics of epidemiology; the theme is statistical association and cause-effect relationship. The primary objective in an epidemiological study is to judge whether an observed association between exposure and disease is real and; indeed; causal. The role of chance and its statistical quantification in explaining an observed association is presented; discussion sampling variation and inference; and interpretation of the frequently quoted P-value. The potential role of bias and confounding is presented; discussing the main categories of bias. Finally; positive criteria useful in supporting a cause and effect judgement; on an observed statistical assoication are enumerated and discussed