1 Answers
In probability and statistics, the base rate is the class of probabilities unconditional on "featural evidence".
For example, if it were the case that 1% of the public were medical professionals, and 99% of the public were not medical professionals, then the base rate of medical professionals is simply 1%. The normative method for integrating base rates and featural evidence is given by Bayes' rule.
In the sciences, including medicine, the base rate is critical for comparison. It may be perceived as impressive that 1,000 people recovered from their winter cold while using 'Treatment X', until the entirety of the 'Treatment X' population is evaluated to find that the base rate of success is only 1/100. The treatment's effectiveness is clearer when such base rate information is available. Note that controls may likewise offer further information for comparison; for example, this would be the case if the control groups, who were using no treatment at all, had their own base rate success of 5/100. This would indicate that 'Treatment X' makes things worse, despite the initial claim bringing attention to the 1,000 people.