Gurland, John; Tripathi, Ram C. (1971), "A Simple Approximation for Unbiased Estimation of the Standard Deviation", The American Statistician, 25 (4): 30–32, doi:10.2307/2682923, JSTOR2682923
Shiffler, Ronald E.; Harsha, Phillip D. (1980). "Upper and Lower Bounds for the Sample Standard Deviation". Teaching Statistics. 2 (3): 84–86. doi:10.1111/j.1467-9639.1980.tb00398.x.
Gurland, John; Tripathi, Ram C. (1971), "A Simple Approximation for Unbiased Estimation of the Standard Deviation", The American Statistician, 25 (4): 30–32, doi:10.2307/2682923, JSTOR2682923