← All parts of this equation

Equation 19 · Part 1 · Measuring What a RAG System Retrieves, Not Just What It Answers

Symbol P

P(correct)  =  P(R) P(correct∣R)⏟grounded in retrieved evidence  +  P(¬R) P(correct∣¬R)⏟correct without sufficient retrieved evidenceP(\text{correct}) \;=\; \underbrace{P(R)\,P(\text{correct} \mid R)}_{\text{grounded in retrieved evidence}} \;+\; \underbrace{P(\lnot R)\,P(\text{correct} \mid \lnot R)}_{\text{correct without sufficient retrieved evidence}}
PP

What this part means

P is part of the quantity the equation computes from the expression on the right.

Its job in the formula

P is part of the quantity the equation computes from the expression on the right.

The passage around this formula

…score measures the left-hand side only. The two terms on the right are exactly what generation metrics and retrieval metrics separately illuminate, and the second term is the one an aggregate score cannot see at all. P(correct\text{correct} ∣\mid ¬\lnot R) is the probability the model answers correctly despite the retriever having failed — because the underlying language model already carried the answer parametrically, because the question was easy enough to guess, or, in the worst case, because the benchmark’s own…

Read this part in the article →

Learn the underlying idea

A function assigns an output to each allowed input. The expression f(x) means “apply f to x”.

Open the illustrated functions: inputs become outputs guide →

See this notation across published equations →

Sources cited in the article section

These citations provide research context; check each source for the exact claim it supports.