Joe - I think it has something to do with tests using interaction "#" notation. Here's a test .do file I was using:
Contains data from testtime.dta
obs: 1,764
vars: 6 30 Dec 2009 11:00
size: 28,224 (99.9% of memory free)
----------------------------------------------------------------------------------------------------
storage display value
variable name type format label variable label
----------------------------------------------------------------------------------------------------
itime int %9.0g
icyt int %8.0g
jsub int %8.0g
ished byte %8.0g
z float %9.0g
icon byte %8.0g
----------------------------------------------------------------------------------------------------
Sorted by:
. summ
Variable | Obs Mean Std. Dev. Min Max
-------------+--------------------------------------------------------
itime | 1764 2 .8167281 1 3
icyt | 1764 11 6.057018 1 21
jsub | 1764 43.78571 46.23181 1 110
ished | 1764 .3571429 .4792933 0 1
z | 1698 2.161716 1.369204 -2.302585 6.79425
-------------+--------------------------------------------------------
icon | 1764 .3571429 .4792933 0 1
//testtime.do
version 9.0
args NIT
use testtime,clear
forv it=1(1)`NIT' {
timer clear 1
timer on 1
forv i=1(1)21 {
xtreg z itime##ished icon if icyt==`i' ,i(jsub)
lincom _b[2.itime#1.ished] -_b[1.itime#1.ished] + _b[2.itime]-_b[1.itime]
lincom _b[3.itime#1.ished] -_b[1.itime#1.ished] + _b[3.itime]-_b[1.itime]
lincom _b[3.itime#1.ished] -_b[2.itime#1.ished] + _b[3.itime]-_b[2.itime]
}
timer off 1
timer list 1
noi di `it',r(t1)
}
and here's the timings for the first 51 iterations:
1 .937
2 .922
3 .953
4 .985
5 1
6 1.046
7 1.063
8 1.109
9 1.157
10 1.203
11 1.25
12 1.328
13 1.36
14 1.406
15 1.5
Now I run it again without the "lincoms" (closing out all Stata processes and launching it again):
. run testtime 15
1 .859
2 .844
3 .844
4 .859
5 .844
6 .844
7 .844
8 .859
9 .859
10 .844
11 .86
12 .843
13 .844
14 .86
15 .875
Al
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