*
* Example 8.5, page 281
* MWD test for functional form
*
cal(q) 1971:1
open data table7-6.prn
data(format=prn,org=columns) 1971:1 1975:2
*
set logy  = log(y)
set logx2 = log(x2)
set logx3 = log(x3)
*
* MWD (MacKinnon-White-Davidson) test for functional form
*
linreg y
# constant x2 x3
prj yhat
*
linreg logy
# constant logx2 logx3
prj logyhat
*
* Test linear functional form
*
set loggap = log(yhat)-logyhat
linreg y
# constant x2 x3 loggap
exclude(title="MWD Test for Linear vs Log-Linear")
# loggap
*
* Test log functional form
*
set lingap = exp(logyhat)-yhat
linreg logy
# constant logx2 logx3 lingap
exclude(title="MWD Test for Log-Linear vs Linear")
# lingap