有关RR和OR的异同的权威解释

Some studies use relative risks (RRs) to describe results; others use odds ratios (ORs). Both are calculated from simple 2x2 tables. The question of which statistic to use is subtle but very important.

Relative risk

Probability is the likelihood of an event in relation to all possible events. If a horse wins 2 out of every 5 races, its probability of winning is 2/5 (40%).

Relative risk is a ratio of probabilities. It compares the incidence or risk of an event among those with a specific exposure with those who were not exposed (eg, myocardial infarctions in those who smoke cigarettes compared with those who do not) . RR is based upon the incidence of an event given that we already know the study partic-ipants’ exposure status. It is only appropriate, therefore, to use RR for prospective cohort studies.

FIGURE

Source for MI data: Njolstad I, et al. Smoking, serum lipids, blood pressure, and sex differences in myocardial infarction. Circulation 1996; 93:450-456.

Odds ratio

Odds compare events with nonevents. If a horse wins 2 out of every 5 races, its odds of winning are 2 to 3 (expressed as 2:3). An odds ratio is a ratio of ratios. It compares the presence to absence of an exposure given that we already know about a specific outcome (eg, presence-to-absence ratio of cigarette smoking in those who had an MI compared with the same ratio in those who did not have an MI) . OR can be used to describe the results of case control as well as prospective cohort studies.

Comparing the two

OR and RR are usually comparable in magnitude when the disease studied is rare (eg, most can-cers). However, an OR can overestimate and magnify risk, especially when the disease is more common (eg, hypertension) and should be avoided in such cases if RR can be used.

当疾病发生率比较低时，建议采用RR或OR表示。如果是常见疾病，或发生率较高，不推荐用OR，它可能会放大风险。

从这幅图可以清晰看到RR与OR的差别。

著名统计学家Steve Simon曾写了有关二者的权威解释。
MedSci注：一般来说，在流行病学研究领域，进行case control研究，建议使用OR，而队列研究则建议使用RR。对于横断面研究，RR和OR都是合适的。但是在临床上并没有极其严格区分，主要根据临床研究的目的与意义，以及选择的统计学方法决定。如采用logistic回归，得出的就是OR。