在流行病学研究中，经常会遇到这几个词，患病率，发病率，你是不是有点晕乎乎的呀，别担心，我这里就来为你解答。

患病率（Prevalence），是指某一时点/时段，某种医疗状态（疾病或危险因素）的人在特定人群中的比例。

Prevalence in epidemiology is the proportion of a particular population found to be affected by a medical condition (typically a disease or a risk factor such as smoking or seat-belt use). It is arrived at by comparing the number of people found to have the condition with the total number of people studied, and is usually expressed as a fraction, as a percentage, or as the number of cases per 10,000 or 100,000 people.

发病率（Incidence），是指某一时段内，新增的患有某种医疗状态的人在特定人群中所占的比例。

Incidence in epidemiology is a measure of the probability of occurrence of a given medical condition in a population within a specified period of time. Although sometimes loosely expressed simply as the number of new cases during some time period, it is better expressed as a proportion or a rate with a denominator.

死亡率（mortality rate or death rate），是指在特定人群中死亡人数的度量方式。

Mortality rate, or death rate, is a measure of the number of deaths (in general, or due to a specific cause) in a particular population, scaled to the size of that population, per unit of time.