The variance error of the P50-discriminant

The P₅₀-discriminant has been reported elsewhere in connection with its use in predicting whether selective service registrants if inducted would become normal operative soldiers or would commit offenses causing their imprisonment. The standard error of the P₅₀-discriminant is a good measure to use in determining how far to the side of this statistic a particular case falls. The standard error formula itself has also been published elsewhere; but its derivation, as the variance error, is given here.The author gratefully acknowledges the very extensive assistance kindly given to him by Dr. Truman L. Kelley and Dr. Frederick Mosteller. This assistance was given without reference to the utility of the P₅₀-discriminant, upon which matter the author reports elsewhere and for which he takes full responsibility.