No! — and the difference matters. Both terms appear constantly in scientific articles, often as synonyms. They are not. A surgical example makes it clear: out of every 100 esophagectomies, 7 patients die postoperatively.
The event divided by all possibilities: 7 deaths among 100 patients.
7 / 100 = 7%The event divided by its non-occurrence: 7 deaths for 93 survivors.
7 : 93 = 0.075In a coin toss: the probability of heads is ½ (50%); the odds are 1:1. Measures such as postoperative mortality, complication rate and risk of dehiscence are probabilities; the odds ratio of case-control studies is odds.
Because the sample is assembled from the outcome: disease frequencies do not reflect the population, and only the odds ratio remains valid.
When the outcome is rare (rule of thumb: prevalence below ~10%), OR and RR are numerically close.
The odds of the event in the exposed group are twice the odds in the unexposed group — odds, not probability.
Written by Francisco Tustumi, digestive system surgeon (FMUSP), associate editor of ABCD.
Developed by Surya MKT