Box-Cox Variance-Stabilizing Transformations Question--A common assumption in regression, ANOVA, etc. is that sd(Y) is constant; if sd(Y) is not constant, then what transformation T(Y) will yield sd(T(Y)) = constant. Answer--T(Y) = integral 1 / sd(Y) = integral 1 / (Y*relsd(Y)) resd(Y) sd(Y) T(Y) ----------------------------------------- Y Y**(2) Y**(-1) Y**(1/2) Y**(3/2) Y**(-1/2) constant Y log(Y) Y**(-1/2) Y**(1/2) Y**(1/2) Y**(-1) constant Y (no trans.) Y**(-3/2) Y**(-1/2) Y**(3/2) Y**(-2) Y**(-1) Y**2