One can always use the delta method (statistical differentials) for problem of that sort, but in case the idea is to compute a confidence interval, intervals based on asymptotic normality should be computed in the scale where normality is most plausible, likely logit in this case, and the bounds transformed as needed.
r-sig-ecology-boun...@r-project.org wrote on 07/08/2010 07:52:14 AM: > From: > > Manuel Spínola <mspinol...@gmail.com> > > To: > > r-sig-ecology@r-project.org > > Date: > > 07/08/2010 07:56 AM > > Subject: > > [R-sig-eco] Transforming logits to probabilities > > Dear list members, > > I am using function invlogit from the "arm" package to get the > difference in probabilities for a explanatory factor from the model > below (I am working with factor "iluminacion"). > > > invlogit(-0.4241 - 0.4804 * 0) - invlogit(-0.4241 - 0.4804 * 1) # > difference in probability for iluminacion > [1] 0.1074094 > > How can I transform the standard error of the difference from logit to > probability? > > The standard error in logits is 0.2416 (taken from the model below). > > Best, > > Manuel > > > > summary(mod6) > > Call: > glm(formula = condicion ~ iluminacion + animales + cielo.raso + > piso + paredes, family = binomial, data = reglog) > > Deviance Residuals: > Min 1Q Median 3Q Max > -1.2527 -1.0034 -0.8276 1.2208 1.6981 > > Coefficients: > Estimate Std. Error z value Pr(>|z|) > (Intercept) -0.4241 0.2833 -1.497 0.1343 > iluminacion[T.1] -0.4804 0.2416 -1.988 0.0468 * > animales[T.1] 0.4613 0.2385 1.934 0.0531 . > cielo.raso[T.1] -0.1386 0.2840 -0.488 0.6254 > piso[T.1] 0.1380 0.2934 0.470 0.6382 > paredes[T.1] -0.1289 0.3012 -0.428 0.6687 > --- > Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1 > > (Dispersion parameter for binomial family taken to be 1) > > Null deviance: 433.04 on 319 degrees of freedom > Residual deviance: 424.30 on 314 degrees of freedom > (25 observations deleted due to missingness) > AIC: 436.3 > > Number of Fisher Scoring iterations: 4 > > > -- > Manuel Spínola, Ph.D. > Instituto Internacional en Conservación y Manejo de Vida Silvestre > Universidad Nacional > Apartado 1350-3000 > Heredia > COSTA RICA > mspin...@una.ac.cr > mspinol...@gmail.com > Teléfono: (506) 2277-3598 > Fax: (506) 2237-7036 > > _______________________________________________ > R-sig-ecology mailing list > R-sig-ecology@r-project.org > https://stat.ethz.ch/mailman/listinfo/r-sig-ecology [[alternative HTML version deleted]]
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