*
* Example 4.7 from page 135
*
open data jtrain.raw
data(format=free,org=columns) 1 471 year fcode employ sales avgsal scrap rework tothrs union grant d89 $
 d88 totrain hrsemp lscrap lemploy lsales lrework lhrsemp lscrap_1 grant_1 clscrap cgrant clemploy clsales $
 lavgsal clavgsal cgrant_1 chrsemp clhrsemp
*
* The sample is 30 observations in the middle of the data set with year==1987
*
linreg(smpl=(year==1987)) lscrap 187 400
# constant hrsemp lsales lemploy