Hello,
I am using Stata 14 w/ 64M memory. Essentially, I am running a joint test of significance and after running it a few times, have noticed that my p-values and f-statistics are changing slightly iteration to iteration.
For more detail: I'm running a joint regression with a panel of stacked outcomes and then testing coefficients against each other, similar to what's described here. Essentially, I have stacked all my data across all my different outcomes into a single regression, and then created explanatory variables so that every single regression coefficient from all the separate regressions appears in this single regression. I then interact each of the explanatory variables with outcome type dummies, and also include the uninteracted outcome type dummies. This results in a dataset with 300k+ observations.
The code is something like:
Then I store these local macros into a table using putexcel (v14). However, I noticed that when I ran this 3-4 times, I got slightly different results for my p-values and the F-stats. For example, on one iteration my F was 1.7588 and on another it was 1.7590. On another my p-value was 0.0694, and the second time I ran it it was 0.0692.
I have reviewed my code several times and I'm unsure of why this would be changing. Is there something changing in the way Stata is storing these values (perhaps it's using up so much memory that Stata changes the way it's rounding)? There are some dummies that are being dropped due to collinearity, and I thought maybe the random variables that got dropped were affecting the p's and F's,but after reading about this it doesn't seem like it should change the outcomes. Any other ideas?
Thank you!
Lucia
I am using Stata 14 w/ 64M memory. Essentially, I am running a joint test of significance and after running it a few times, have noticed that my p-values and f-statistics are changing slightly iteration to iteration.
For more detail: I'm running a joint regression with a panel of stacked outcomes and then testing coefficients against each other, similar to what's described here. Essentially, I have stacked all my data across all my different outcomes into a single regression, and then created explanatory variables so that every single regression coefficient from all the separate regressions appears in this single regression. I then interact each of the explanatory variables with outcome type dummies, and also include the uninteracted outcome type dummies. This results in a dataset with 300k+ observations.
The code is something like:
Code:
regress y x1 x2 x3 dummies controls interaction terms test x1 = x2 loc F_x1 = `r(F)' loc p_x1 = `r(p)' test x2 = x3 loc F_x2 = `r(F)' loc p_x3 = `r(p)'
Then I store these local macros into a table using putexcel (v14). However, I noticed that when I ran this 3-4 times, I got slightly different results for my p-values and the F-stats. For example, on one iteration my F was 1.7588 and on another it was 1.7590. On another my p-value was 0.0694, and the second time I ran it it was 0.0692.
I have reviewed my code several times and I'm unsure of why this would be changing. Is there something changing in the way Stata is storing these values (perhaps it's using up so much memory that Stata changes the way it's rounding)? There are some dummies that are being dropped due to collinearity, and I thought maybe the random variables that got dropped were affecting the p's and F's,but after reading about this it doesn't seem like it should change the outcomes. Any other ideas?
Thank you!
Lucia