“The Limits of a Measure of Skewness”, Harold Hotelling, Leonard M. Solomons1932-05-01 (; similar)⁠:

[Peyman: The Mean (μ) and median (m) of any distribution (with finite variance) are at most one standard deviation (σ) apart:

|μ − m| ≤ σ

It was written up around the same time by C. Mallows in “Another comment on O’Cinneide”, The American Statistician, 45-3, using Jensen’s inequality twice. If the distribution is unimodal:

|μ − m| ≤ √3⁄5 σ]