Tight bounds for the median of a gamma distribution.

Lyon, Richard F · PLoS One · 2023

basic_science · Level V

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Abstract

The median of a standard gamma distribution, as a function of its shape parameter k, has no known representation in terms of elementary functions. In this work we prove the tightest upper and lower bounds of the form 2-1/k(A + k): an upper bound with A = e-γ (with γ being the Euler-Mascheroni constant) and a lower bound with [Formula: see text]. These bounds are valid over the entire domain of k > 0, staying between 48 and 55 percentile. We derive and prove several other new tight bounds in support of the proofs.