*! version 1 15Oct2014

Title

reg_distdicho-- The distributional method for regression results
to obtain comparison of proportions adjusted for covariates.
reg_distdicho will provide the distributional estimate after a regression
model has been fitted.

Syntax

Distributional estimates for marginal effect estimates

reg_distdicho
varname
[, options]

options

Main
cp value of the cut-point under which to compute proportions

tail provides the tail of the distribution in which the proportions are computed

where varname is a dichotomous factor variable that
appears in the current estimation results.

Description

reg_distdicho presents the distributional estimates and their standard errors
(see Sauzet et al 2013 and Peacock et al 2012) for a difference in proportion,
risk ratio and odds ratio for the two groups as well as providing the distributional
95% confidence interval for the statistics estimated using marginal effects of
a linear (mixed) model.

Options

Main

cp specifies the cutpoint under which the distributional proportions in group1
and group2 are computed using the distributional method described in Peacock et al.
cp requires a real number. When no value is given a cutpoint of 0 is used.

tail provides the tail of the distribution in which the proportions are to
be computed. The default is the lower tail, upper will provide estimates
in the upper tail.

Remarks

To use this method results of a linear (mixed) model (e.g. of regress,
xtmixed or xtreg) must be in the current saved results.

Examples

setup

. webuse bwsmoke

Proportions of low birthweight babies among smoking and non-smoking mothers

Model fitted by regress

. regress birthwt i.smoke gest if babycon==1 & gest >=37

. reg_distdicho smoke, tail(lower) cp(2500)

setup

. webuse bw_mixed

Model fitted by xtmixed

. xtmixed birthwt i.smoke age birthorder, ||mother:

. reg_distdicho smoke, tail(lower) cp(2500)

Model fitted by xtreg

. xtreg birthwt i.smoke age birthorder, i(mother)

. reg_distdicho smoke, tail(lower) cp(2500)

Stored results

reg_distdicho stores the following in r():

Scalars

r(prop1) distributional proportion estimate for group1

r(prop2) distributional proportion estimate for group2

r(propdiff) distributional estimate for the difference in proportions between group1 and group2

r(distrr) distributional estimate for risk ratio between group1 and group2

r(distor) distributional estimate for odds ratio between group1 and group2

r(sediff) standard error for the distributional estimate of the difference in proportion

r(serr) standard error for the distributional estimate of the risk ratio

r(seor) standard error for the distributional estimate of the odds ratio

r(ciinf) difference in proportions: lower limit of the 95% confidence interval

r(cisup) difference in proportions: upper limit of the 95% confidence interval

r(ciinfrr) risk ratio: lower limit of the 95% confidence interval

r(cisuprr) risk ratio: upper limit of the 95% confidence interval

r(ciinfor) odss ratio: lower limit of the 95% confidence interval

r(cisupor) odds ratio: upper limit of the 95% confidence interval

References

Peacock J.L., Sauzet O., Ewings S.M., Kerry S.M. Dichotomising continuous data while retaining statistical power using a distributional approach. Statist. Med; 2012;26:3089-3103.
Sauzet, O., Peacock, J. L. Estimating dichotomised outcomes in two groups with unequal variances: a distributional approach. Statist. Med; 2014;DOI: 10.1002/sim.6255.

Authors

Odile Sauzet, Universität Bielefeld

odile.sauzet@uni-bielefeld.de

Maren Kleine, Universität Bielefeld