* brief do-file for GO Problem 8.1, VHM 802
version 18 /* works also with versions 14-17 */
set more off
set scheme stcolor_alt
cd "r:\"

import delimited ch08ta1.csv, clear
anova seeds age##water
predict pred, xb
predict stdres, rstandard
scatter stdres pred
* fan/cone shape

xi: boxcox seeds i.age*i.water
generate rootseed=sqrt(seeds)
generate asinrseed=asin(sqrt(seeds/100))
capture drop pred stdres
anova rootseed age##water
predict pred, xb
predict stdres, rstandard
scatter stdres pred
capture drop pred stdres
anova asinrseed age##water
predict pred, xb
predict stdres, rstandard
scatter stdres pred

* presentation from square-root scale factorial model
anova rootseed age##water
margins age water, asbalanced
margins age, asbalanced plot

* age as quantitative
anova rootseed water age
anova rootseed water c.age
regress
anova rootseed water c.age##c.age, sequential
regress

* presentation from square-root scale model with age effect linear
anova rootseed water c.age
margins water, over(age) expression(predict(xb)^2)
marginsplot, noci x(age)