Code:
. sysuse nlsw88 . qui recode grade (0/8 = 1) (9/12 = 2) (12/max=3), gen(educ) . logit c_city ibn.educ, nocons ------------------------------------------------------------------------------ c_city | Coef. Std. Err. z P>|z| [95% Conf. Interval] -------------+---------------------------------------------------------------- educ | 1 | -.9555114 .2631174 -3.63 0.000 -1.471212 -.4398108 2 | -.9834933 .0647227 -15.20 0.000 -1.110348 -.8566391 3 | -.7701687 .0691436 -11.14 0.000 -.9056876 -.6346498 ------------------------------------------------------------------------------
Code:
. contrast {educ -1 0 1} Contrasts of marginal linear predictions Margins : asbalanced ------------------------------------------------ | df chi2 P>chi2 -------------+---------------------------------- educ | 1 0.46 0.4957 ------------------------------------------------ -------------------------------------------------------------- | Contrast Std. Err. [95% Conf. Interval] -------------+------------------------------------------------ educ | (1) | .1853427 .2720507 -.3478669 .7185524 -------------------------------------------------------------- . lincom 3.educ - 1.educ ( 1) - [c_city]1bn.educ + [c_city]3.educ = 0 ------------------------------------------------------------------------------ c_city | Coef. Std. Err. z P>|z| [95% Conf. Interval] -------------+---------------------------------------------------------------- (1) | .1853427 .2720507 0.68 0.496 -.3478669 .7185524 ------------------------------------------------------------------------------
Code:
. margins i.educ Adjusted predictions Number of obs = 2,244 Model VCE : OIM Expression : Pr(c_city), predict() ------------------------------------------------------------------------------ | Delta-method | Margin Std. Err. z P>|z| [95% Conf. Interval] -------------+---------------------------------------------------------------- educ | 1 | .2777778 .0527859 5.26 0.000 .1743193 .3812362 2 | .2721992 .012822 21.23 0.000 .2470685 .2973299 3 | .3164426 .0149562 21.16 0.000 .287129 .3457563 ------------------------------------------------------------------------------ . margins {educ -1 0 1} Contrasts of adjusted predictions Model VCE : OIM Expression : Pr(c_city), predict() ------------------------------------------------ | df chi2 P>chi2 -------------+---------------------------------- educ | 1 0.50 0.4810 ------------------------------------------------ -------------------------------------------------------------- | Delta-method | Contrast Std. Err. [95% Conf. Interval] -------------+------------------------------------------------ educ | (1) | .0386648 .0548638 -.0688663 .146196 -------------------------------------------------------------- . nlcom invlogit(_b[3.educ]) - invlogit(_b[1.educ]) _nl_1: invlogit(_b[3.educ]) - invlogit(_b[1.educ]) ------------------------------------------------------------------------------ c_city | Coef. Std. Err. z P>|z| [95% Conf. Interval] -------------+---------------------------------------------------------------- _nl_1 | .0386648 .0548638 0.70 0.481 -.0688663 .146196 ------------------------------------------------------------------------------
Since I am most interested in directly estimating the change in probability, rather than the change in odds, should inferences be made then on the probability scale? Or would I needlessly be sacrificing precision by not staying in the log-odds scale?
0 Response to Reporting contrasts of marginal effects from logit/probit models
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