Base Rate Calculator
From raw numbers to clear insight: calculate the true probability behind a positive test result and see why base rates matter. Perfect for students, journalists, and data analysts who want to avoid the base rate fallacy.
Results update live as you type — no button needed. The Example button fills a sample input.
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Why use Base Rate Calculator?
Instantly compute base rates and conditional probabilities from raw counts
Understand the impact of false positives and false negatives
Avoid common statistical misconceptions like the base rate fallacy
Clear explanations accompany every result
Works with any probability expression using standard arithmetic
FAQ
What is a base rate?
The base rate is the underlying probability of an event in a population before any new evidence is considered. For example, the prevalence of a disease in a population.
What is the base rate fallacy?
The base rate fallacy is the tendency to ignore the base rate (prior probability) when evaluating new evidence, leading to incorrect conclusions about conditional probabilities.
How do I calculate the probability of a true positive given a positive test result?
Use Bayes' theorem: P(disease | positive) = (P(positive | disease) * P(disease)) / P(positive). Our calculator helps you compute this from raw counts.
Can I use this calculator for any conditional probability problem?
Yes, as long as you can express the problem as a mathematical expression involving counts or probabilities. The calculator evaluates standard arithmetic expressions.