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Re: st: create one factor level from two existing


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: create one factor level from two existing
Date   Wed, 26 Dec 2012 19:02:57 +0000

This should help:

SJ-7-4  dm0034  . . . Stata tip 52: Generating composite categorical variables
        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
        Q4/07   SJ 7(4):582--583                                 (no commands)
        tip on how to generate categorical variables using
        tostring and egen, group()

A .pdf version is accessible at

http://www.stata-journal.com/sjpdf.html?articlenum=dm0034

Nick

On Wed, Dec 26, 2012 at 5:37 PM, Lane, Scott D <Scott.D.Lane@uth.tmc.edu> wrote:

> I have a design with 2 placebo (plc) doses (a baseline plc, designated 1, to familiarize/stabilize subjects on a lab task) plus three CNS-active doses and an additional plc dose (designated 2-5 and counterbalanced).  Performance on the 2 placebo doses is highly correlated and I thus wish the combine the 2 placebos into 1 plc factor in the analytic model (e.g., dose with 4 levels).  In the .dat file, the data are in long format with several other DVs and IVs for each subject.  Please advise re: how to use egen (or some other technique) to pull this off?  To date, I have tried:
> 1. egen rowmeans for each of the 2 plc doses, then attempted, by subject, to average the 2 newly created variables (result = a variable of blank values).
> 2. reshape to wide format, then use egen rowmeans (result = error message stating that most of the other IVs and DVs cannot be reshaped to wide format).  Thus, I cannot get started without deleting many other variables.
>

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