cd "/Users/steve/Documents/teaching/c2014/biostat208/labs/lab3/"
* do "/Users/steve/Documents/teaching/c2014/biostat208/labs/lab3/lab3.do"

log using lab3, replace
use lab3, clear

tab physact, sum(bmi)
reg bmi i.physact
* compute mean BMI at each level of physact
forvalues i = 2/5 {
lincom _cons + `i'.physact
}
margins physact

* test for heterogeneity
testparm i.physact
* test for linear trend
contrast q(1).physact, noeffects
* test for departure from linear trend
contrast q(2/4).physact, noeffects

* repeat with adjustment for age, smoking, and alcohol use
reg bmi i.physact age10 smoking drnkspwk
* compute mean BMI at each level of physact
margins physact, atmeans
* test for heterogeneity
testparm i.physact
* test for linear trend
contrast q(1).physact, noeffects
* test for departure from linear trend
contrast q(2/4).physact, noeffects

* models using log of creatinine level as outcome and predictor
regress lncreat bmi age, eform("exp(beta)")
nlcom 100*(exp(_b[bmi])-1)
regress sbp lncreat age diabetes
nlcom _b[lncreat]*log(1.25)

log close