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Re: st: Confirming whether a variable is binary or continuous

From   Nick Cox <>
Subject   Re: st: Confirming whether a variable is binary or continuous
Date   Fri, 16 Mar 2012 22:30:32 +0000

-distinct- is also from SJ. The paper

SJ-8-4  dm0042  . . . . . . . . . . . .  Speaking Stata: Distinct observations
        (help distinct if installed)  . . . . . .  N. J. Cox and G. M. Longton
        Q4/08   SJ 8(4):557--568
        shows how to answer questions about distinct observations
        from first principles; provides a convenience command

is in effect a review of this and related questions.


On Fri, Mar 16, 2012 at 9:28 PM, Eric Booth <> wrote:

> One way is to -tabulate- the var and then use stored value in r(r) to tell how many values it has.  You could also grab values from the user-written packages -egenmore- (form SJ, see the nvals() fcn) and -distinct- (from SSC)
> Example:
> *********
> sysuse auto, clear
> ds, has(type numeric)
> foreach x in `r(varlist)' {
> quietly tabulate `x'
> if r(r) == 2 di in red `"`x' is binary"'
> if r(r)!=2  di "`x'  is not binary"
> }
> *********

On Mar 16, 2012, at 4:18 PM, Bert Jung wrote:

>> I am writing a short program to make a balance table that compares
>> covariates across a treatment and control group.  I am looking for a
>> way to confirm whether a variable is binary in order to use -prtest-
>> for proportions rather than -ttest- for continous variables.
>> One option is to check the actual data values and do -prtest- if there
>> are only 0's and 1's.  But a continuous but rare outcome could
>> accidentally also take these values, e.g. the number of
>> hospitalizations in the past 3 months.
>> Is there a safer way to confirm that a variable is binary?

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