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From |
Urmi Bhattacharya <ub3@indiana.edu> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Query about finding predicted change in probability after logit for changing two variables |

Date |
Fri, 10 Jun 2011 11:25:43 -0400 |

Hi Austin, Thank you so much for both your responses. I understand I need to calculate the change in predicted probability at each duration of risk separately, using only the sample of people who are at risk in the duration. So I need to modify the code below in such a way do as to figure out how to do the same for a subset of the sample which is what i am struggling to do. However, when i run the code below just as you have typed it,I get the following error message: u if rep78<. using `c(sysdir_base)'a/auto (1978 Automobile Data) . . g byte medium=inlist(rep78,3,4) . g byte high=inlist(rep78,5) . g byte turnhi=(turn>35) . logit foreign high medium turnhi headroom mpg trunk Iteration 0: log likelihood = -42.400729 Iteration 1: log likelihood = -26.95755 Iteration 2: log likelihood = -25.645315 Iteration 3: log likelihood = -25.378962 Iteration 4: log likelihood = -25.326588 Iteration 5: log likelihood = -25.315298 Iteration 6: log likelihood = -25.313291 Iteration 7: log likelihood = -25.312837 Iteration 8: log likelihood = -25.312726 Iteration 9: log likelihood = -25.312703 Iteration 10: log likelihood = -25.312698 Iteration 11: log likelihood = -25.312697 Logistic regression Number of obs = 69 LR chi2(6) = 34.18 Prob > chi2 = 0.0000 Log likelihood = -25.312697 Pseudo R2 = 0.4030 ------------------------------------------------------------------------------ foreign | Coef. Std. Err. z P>|z| [95% Conf. Interval] -------------+---------------------------------------------------------------- high | 19.23396 2458.202 0.01 0.994 -4798.753 4837.221 medium | 16.98224 2458.202 0.01 0.994 -4801.005 4834.969 turnhi | -1.44119 .9947506 -1.45 0.147 -3.390866 .508485 headroom | -.5846668 .6258184 -0.93 0.350 -1.811248 .6419148 mpg | -.0071336 .0863283 -0.08 0.934 -.1763339 .1620667 trunk | -.1430355 .1284915 -1.11 0.266 -.3948742 .1088032 _cons | -13.22992 2458.203 -0.01 0.996 -4831.22 4804.76 ------------------------------------------------------------------------------ Note: 6 failures and 0 successes completely determined. . replace medium=1 (21 real changes made) . replace high=0 (11 real changes made) . replace turnhi=0 (55 real changes made) . predict p1 (option pr assumed; Pr(foreign)) . replace medium=0 (69 real changes made) . replace high=1 (69 real changes made) . replace turnhi=1 (69 real changes made) . predict p2 (option pr assumed; Pr(foreign)) . g dp=p2-p1 . . mat dp=r(mean) . loc n=r(N) . prog drop _all . prog mymarg, rclass 1. u if rep78<. using `c(sysdir_base)'a/auto, clear 2. bsample 3. g byte medium=inlist(rep78,3) 4. g byte high=inlist(rep78,45) 5. g byte turnhi=(turn>35) 6. logit foreign high medium turnhi headroom mpg trunk 7. replace medium=1 8. replace high=0 9. replace turnhi=0 10. predict p1 11. replace medium=0 12. replace high=1 13. replace turnhi=1 14. predict p2 15. g dp=p2-p1 16. su dp, mean 17. ret scalar dp=r(mean) 18. eret clear 19. end . simulate, reps(141) seed(123): mymarg command: mymarg dp: r(dp) Simulations (141) ----+--- 1 ---+--- 2 ---+--- 3 ---+--- 4 ---+--- 5 ...............x...x.......x............x......... 50 .........................x........................ 100 .........x.................x............. . bstat, stat(dp) n(`n') estimates post: matrix has missing values r(504); end of do-file r(504); Looking at the error code it says [P] error . . . . . . . . . . . . . . . . . . . . . . . . Return code 504 matrix has missing values; You have issued a matrix command attempting a matrix operation that, were it carried out, would result in a matrix with missing values; dividing by zero is a good example. I was wondering if you could tell me why am I getting this? I wanted to get this code to work, so that i can try and modify it to get the change in predicted probability for subsamples of the dataset. Thank you so much for your kind advice on this so far. Best Urmi On Thu, Jun 9, 2011 at 3:20 PM, Austin Nichols <austinnichols@gmail.com> wrote: > Urmi Bhattacharya <ub3@indiana.edu> wrote: > "now i want to find what is the predicted change in the > probability of foreign for those cars with cqual_high=1 with > turn_high=1 from those with cqual_medium=1 and turn_low=1" > > The meaning of the above is totally unclear to me, > and I cannot understand you cqual_ coding is supposed to be, > but perhaps you mean to: > compare (1) medium==1 and turnhi==0 > to (2) high==1 and turnhi==1 > like so: > > clear all > u if rep78<. using `c(sysdir_base)'a/auto > g byte medium=inlist(rep78,3,4) > g byte high=inlist(rep78,5) > g byte turnhi=(turn>35) > logit foreign high medium turnhi headroom mpg trunk > replace medium=1 > replace high=0 > replace turnhi=0 > predict p1 > replace medium=0 > replace high=1 > replace turnhi=1 > predict p2 > g dp=p2-p1 if e(sample) > su dp, mean > mat dp=r(mean) > loc n=r(N) > prog drop _all > prog mymarg, rclass > u if rep78<. using `c(sysdir_base)'a/auto, clear > bsample > g byte medium=inlist(rep78,3) > g byte high=inlist(rep78,45) > g byte turnhi=(turn>35) > logit foreign high medium turnhi headroom mpg trunk > replace medium=1 > replace high=0 > replace turnhi=0 > predict p1 > replace medium=0 > replace high=1 > replace turnhi=1 > predict p2 > g dp=p2-p1 if e(sample) > su dp, mean > ret scalar dp=r(mean) > eret clear > end > simulate, reps(141) seed(123): mymarg > bstat, stat(dp) n(`n') > > *But I want to reiterate that you should look at each duration's risk > set separately: > http://www.stata.com/statalist/archive/2011-06/msg00465.html > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: Query about finding predicted change in probability after logit for changing two variables***From:*Urmi Bhattacharya <ub3@indiana.edu>

**References**:**st: Query about finding predicted change in probability after logit for changing two variables***From:*Urmi Bhattacharya <ub3@indiana.edu>

**Re: st: Query about finding predicted change in probability after logit for changing two variables***From:*Austin Nichols <austinnichols@gmail.com>

**Re: st: Query about finding predicted change in probability after logit for changing two variables***From:*Urmi Bhattacharya <ub3@indiana.edu>

**Re: st: Query about finding predicted change in probability after logit for changing two variables***From:*Austin Nichols <austinnichols@gmail.com>

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