Bias of Estimator for Cp
/****************************************************************/
/* S A S S A M P L E L I B R A R Y */
/* */
/* NAME: CPBIAS */
/* TITLE: Bias of Estimator for Cp */
/* PRODUCT: QC */
/* SYSTEM: ALL */
/* KEYS: Capability Analysis, Capability Indices, */
/* PROCS: G3D */
/* DATA: */
/* */
/* REF: W. L. Pearn, S. Kotz, N. L. Johnson (1992). */
/* "Distributional and Inferential Properties of */
/* Process Capability Indices". Journal of Quality */
/* Technology 24, pp. 216-231. */
/* */
/* NOTES: This program calculates the bias for the estimator */
/* of Cp using results of Pearn et al. (1992) */
/* */
/* MISC: */
/* */
/****************************************************************/
options ps=60 ls=80;
data cp;
keep ds n bi;
label n = ' n '
ds = 'd/Sigma'
bi = 'Bias'
;
do ds = 2 to 6 by 0.05;
do n = 30 to 120 by 5;
f = n-1;
tmp = lgamma((f-1)/2) - lgamma(f/2);
ex = exp(tmp)*sqrt((f/2));
ex = (ds/3)*ex;
bi = ex - (ds/3);
output;
end;
end;
run;
axis1 order=(30 to 120 by 30);
title 'Bias of Estimator for Cp';
proc g3d;
plot ds*n = bi /
xticknum = 4
yticknum = 5
zticknum = 5
zmin = 0.00
zmax = 0.06
rotate = 45
tilt = 70
grid
;
run;
goptions reset=all;