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Equation 7 · Part 1 · Measuring AI Agent Reliability: What the Evidence Actually Supports

Symbol k

pass@k  :=  Etasks ⁣[ 1  −  (n−ck)(nk) ]\text{pass@}k \;:=\; \mathbb{E}_{\text{tasks}}\!\left[\, 1 \;-\; \frac{\binom{n-c}{k}}{\binom{n}{k}} \,\right]
kk

What this part means

the number of samples.

Its job in the formula

k is computed from the expected values combined on the right.

Where the article explains it

The obvious approach — generate exactly k samples per problem and check whether any of them pass — has an undesirable property: it is a valid estimate but a high-variance one, since it throws away information every time you happen to generate more or fewer than k samples.

The passage around this formula

…a code-generating model against the HumanEval benchmark, they needed a way to score the strategy of drawing several candidate solutions from the model and keeping the best one. The obvious approach — generate exactly k samples per problem and check whether any of them pass — has an undesirable property: it is a valid estimate but a high-variance one, since it throws away information every time you happen to generate more or fewer than k samples. Their fix was to over-sample: draw n total samples per task,…

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A variable is a named place for a value. Its letter is a local label: x can mean position in one formula and a data point in another.

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Sources cited in the surrounding passage

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