* do-file for Supplementary Exercise 13.31 of IPS7e
version 17 /* works also with versions 13-16 */

import delimited "R:\Chapter 13\ex13_031.csv"
table promo percent, contents( mean eprice sd eprice )
anova eprice promo percent promo#percent
predict pred, xb
sort promo percent
overlay pred percent, by(promo) c(l)
sort percent promo
overlay pred promo, by(percent) c(l)
predict stdres, rstandard
scatter stdres pred
qnorm stdres

* confidence intervals and margins using pwcompare command
pwcompare promo percent, cimargins
pwcompare promo percent, pveffects
pwcompare promo percent, pveffects mcompare(bon)

* t-distribution percentiles for CI and LSD, without/with Bonferroni correction
di invttail(144,.025)
di invttail(144,.025/6)
* confidence intervals and pairwise comparisons can also be done by hand
* percent group means should have a margin of error for a 95% CI of
*   t(.975,144)*0.241648*sqrt(1/40) = 0.076, using a t-value of 1.977
* and the same margin of error applies to promotion means.
* Also, LSD_0.95-values for pairwise comparisons are computed as
*   t(.975,144)*0.241648*sqrt(2/40) = 0.107
* and Bonferroni-corrected LSD values (as in IPS) as follows
*   t(1-0.025/6,144)*0.241648*sqrt(2/40) = 0.145, using a t-value of 2.675