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From |
nagi kayo <kayonagi@hotmail.co.jp> |

To |
statalist質問用 <statalist@hsphsun2.harvard.edu> |

Subject |
RE: st: MIXLPRED: marginal effects after-MIXLOGIT- |

Date |
Fri, 2 Mar 2012 14:40:55 +0900 |

Dear Arne (if I may) Thank you very much for your quick reply and for your question and advice. I am really sorry that I did not provide you with enough information on my application. first, please let me explain the data I used. although the number of "id" used in my estimation is about 10,000, the following is the data on the first two "id." id alt d d1 d2 d3 d1inc d2inc d3inc d4inc p 1 1 1 1 0 0 665 0 0 0 0.214 1 2 0 0 1 0 0 665 0 0 0.186 1 3 0 0 0 1 0 0 665 0 0.381 1 4 0 0 0 0 0 0 0 665 0.219 2 1 0 1 0 0 779 0 0 0 0.553 2 2 1 0 1 0 0 779 0 0 0.301 2 3 0 0 0 1 0 0 779 0 0.107 2 4 0 0 0 0 0 0 0 779 0.039 id: households alt: 1=households are worried about their retirement life because the pension benefit is NOT enough. 2=households are worried about their retirement life for some reasons other than pension. 3=households are NOT worried about their retirement life because the pension benefit is enough. 4=households are NOT worried about their retirement life for some reasons other than pension. d: dummy which equals one if households choose "alt" in the same row. (id 1 chose alt 1, and id 2 chose alt 2.) d1-d3: intercepts d1inc-d4inc: real households income (units of 10,000yen) Mean=531 Std.Dev.=413.4245 Min.=0 Max.=6079.027 p: an alternative specific variable using the above data, i did the estimation as follows: ************************************************ mixlogit d d1 d2 d3 d1inc d2inc d3inc, group(id) rand(p) mixlpred pred_base preserve quietly replace d1inc=d1inc+1 quietly replace d2inc=d2inc+1 quietly replace d3inc=d3inc+1 quietly replace d4inc=d4inc+1 mixlpred pred_inc1 gen dif_inc1=pred_inc1-pred_base sum dif_inc1 if alt==1 sum dif_inc1 if alt==2 sum dif_inc1 if alt==3 sum dif_inc1 if alt==4 restore ************************************************ the results are mean of dif_inc1 is -2.11e-12 if alt==1 mean of dif_inc1 is -1.05e-12 if alt==2 mean of dif_inc1 is 1.87e-12 if alt==3 mean of dif_inc1 is 1.29e-12 if alt==4 i think these marginal effects are too small... so as you kindly advised me, i saw Richard Williams's reply to your earlier post on calculating marginal effects after -mixlogit- and increased by 0.001 and divided the difference by 0.001. ************************************************ mixlogit d d1 d2 d3 d1inc d2inc d3inc, group(id) rand(p) mixlpred pred_base preserve quietly replace d1inc=d1inc+0.001 quietly replace d2inc=d2inc+0.001 quietly replace d3inc=d3inc+0.001 quietly replace d4inc=d4inc+0.001 mixlpred pred_inc2 gen dif_inc2=(pred_inc2-pred_base)/0.001 sum dif_inc2 if alt==1 sum dif_inc2 if alt==2 sum dif_inc2 if alt==3 sum dif_inc2 if alt==4 restore ************************************************ the results are mean of dif_inc1 7.83e-7 if alt==1 mean of dif_inc1 3.85e-7 if alt==2 mean of dif_inc1 -6.64e-7 if alt==3 mean of dif_inc1 -5.04e-7 if alt==4 I think these marginal effects are still too small. finally, I increased the Std.Dev. of the regressor divided by 1,000 and divided the difference by the Std.Dev. of the regressor divided by 1,000. ************************************************ mixlogit d d1 d2 d3 d1inc d2inc d3inc, group(id) rand(p) mixlpred pred_base preserve quietly replace d1inc=d1inc+0.4134245 quietly replace d2inc=d2inc+0.4134245 quietly replace d3inc=d3inc+0.4134245 quietly replace d4inc=d4inc+0.4134245 mixlpred pred_inc3 gen dif_inc3=(pred_inc3-pred_base)/0.4134245 sum dif_inc3 if alt==1 sum dif_inc3 if alt==2 sum dif_inc3 if alt==3 sum dif_inc3 if alt==4 restore ************************************************ the results are mean of dif_inc1 -2.70e-9 if alt==1 mean of dif_inc1 -1.42e-9 if alt==2 mean of dif_inc1 2.24e-9 if alt==3 mean of dif_inc1 1.89e-9 if alt==4 still, the marginal effects are so small. actually, i also controlled the other variables like age and wealth and calculated the marginal effects like above, but their marginal effects are too small, too. so I am wondering if there is something wrong with my calculation. I greatly appreciate it if you would advise me again. with best wishes, Kayo ---------------------------------------- > Date: Wed, 29 Feb 2012 11:01:57 +0000 > Subject: Re: st: MIXLPRED: marginal effects after-MIXLOGIT- > From: arnehole@gmail.com > To: statalist@hsphsun2.harvard.edu > > Dear Kayo, > > It's difficult to help without knowing more about your application. > Most importantly: what is the unit of measurement of the income > variable? If income is measured in dollars or euros (or yen), for > example, you would expect the marginal effect of a one unit increase > in income to be small. See Richard Williams' reply to my earlier post > on calculating marginal effects after -mixlogit-. > > Arne > > 2012/2/29 nagi kayo <kayonagi@hotmail.co.jp>: > > Dear Professor Arne Risa Hole and all > > > > > > > > I read the thread Professor Hole kindly wrote on "Mon, 6 Feb. 2012 13:18:34" about calculating marginal effects after -mixlogit- and tried to calculate marginal effects using the following commands. in my estimation model, the number of alternatives is four, and "inc" is a demographic variable, and "price" is an alternative specific variable. > > > > > > > > mixlogit d d1inc d2inc d3inc, group(id) rand(price) > > mixlpred pred_base > > > > replace d1inc=d1inc+1 > > replace d2inc=d2inc+1 > > replace d3inc=d3inc+1 > > replace d4inc=d4inc+1 > > mixlpred pred_inc > > > > > > however, unexpectedly, "pred_inc" is quite similar to "pred_base," and thus the difference between the two is almost zero, which means that the marginal effect of income is almost zero. > > > > although i also tried the other explanatory variables, the results are not changed (in all cases, marginal effects are almost zero). > > > > is my calculation of predicted probabilities wrong? > > > > > > > > i greatly appreciate it if you would give me your advice. > > > > > > > > with best wishes, > > > > Kayo > > > > > > * > > * For searches and help try: > > * http://www.stata.com/help.cgi?search > > * http://www.stata.com/support/statalist/faq > > * http://! ww w.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/ * * 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: MIXLPRED: marginal effects after-MIXLOGIT-***From:*Arne Risa Hole <arnehole@gmail.com>

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