Introduction
This topic covers how diseases and exposures are measured (ratio, proportion, rate, probability, risk, incidence, prevalence) and how the strength of a risk factor is assessed with the relative risk, attributable risk and odds ratio.
Measurement of disease
In epidemiology and public health many factors and events have only two possible categories: alive or dead, case or control, exposed or unexposed.
- Ratio: quantitative measurement of the relationship between two independent quantities, which may or may not be part of the same denominator, e.g. \frac{\text{male}}{\text{female}}
- Proportion: a ratio in which the numerator is part of the denominator, e.g. \frac{\text{male}}{\text{all}}
- Rate: measures the occurrence of an event in a population over time: \frac{\text{No of cases}}{\text{Pop. at risk}} \times 10^{n}
- Probability: the extent to which an event is likely to happen
- Risk: the probability that an event will occur
- Incidence: the frequency with which new cases of illness occur in a population over a period of time
- Prevalence: all cases regardless of time; measures the distribution of disease in a population at a given moment