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From |
Steve Samuels <sjsamuels@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Standardized difference of means after PS matching |

Date |
Fri, 31 Aug 2012 23:02:59 -0500 |

Adam Olszewski <adam.olszewski@gmail.com>: Your posts give no information that would help anyone to solve your problem. When asked for details, you gave code fragments and made-up numbers. (They are also impossible numbers, as the the SDM's produced by -pblachk- for an xi'd binary variable are of the form -a, +a.) The FAQ state (3.3): "Say exactly what you typed and exactly what Stata typed (or did) in response. N.B. exactly! If you can, reproduce the error with one of Stata's provided datasets or a simple concocted dataset that you include in your posting." Show everything. It will be especially important to see the results of -psmatch2- . You can use any publicly available data set. Also, reduce the number of variables in the -psmatch2- statement to the minimum necessary to observe the problem. I've never used -psmatch2- before, but I've made a brief attempt to replicate your problem, and can't. **************START******************** sysuse auto, clear gen high = mpg>21 //dichotomize mpg set seed 73128 gen u =runiform() sort u tempfile t1 save `t1' /* continuous version of -high- */ psmatch2 foreign high turn price , radius caliper(.2) xi: pbalchk foreign i.high, wt(_weight) use `t1', clear /* xi'd version of -high- */ xi: psmatch2 foreign i.high turn price , radius caliper(.2) xi: pbalchk foreign i.high, wt(_weight) **************END******************* Steve sjsamuels@gmail.com > On Aug 29 2012 17:25:50 -0400, Adam Olszewski wrote: > Subject: Re: st: Standardized difference of means after PS matching > > Hi Ariel, > Thanks for the email. I'll try to clarify: > > I run something like: > . psmatch2 treat age sex i.race ..., (I use radius matching BTW) > . xi: pbalchk treat age i.sex i.race ...., weight(_weight) > > and get output of the kind: > 1.race SDM 0.21 > 2.race SDM 0.18 (I'm making the numbers up but this is the > range) > > Then I try to run: > .psmatch2 treat age sex race ..., (which treats "race" as a > continuous rather than factor variable) > .xi: pbalchk treat age i.sex i.race, weight(_weight) > > and get: > 1.race SDM 0.05 > 2.race SDM 0.06 > > The change between "i.race" and "race" in the psmatch2 model is the > only change I made (I think I initially did it by mistake actually), > and was surprised to see the difference. > I tend not to use -pstest- or other tests that use sample-size > dependent p-values, following PC Austin recommendation. Though perhaps > I should take a look if -pstest- would report any change in bias > reduction. > > On Wed, Aug 29, 2012 at 5:12 PM, Ariel Linden. DrPH > <ariel.linden@gmail.com> wrote: > Hi Adam, > > It is not clear to me what step in your process is giving you different > results? In which program are you using c.race vs i.race? I am not sure that > -pbalchk- (user written program by Mark Lunt) accepts the prefix -c.- and > furthermore, I don't understand why you'd treat a multiple categorical > variable (such as race) as continuous to begin with? You'd certainly end up > with a result that would be meaningless. > > As far as calculating balance on a binary variable (assuming it is binary), > your results should not differ much (between treating the variable as > continuous and eliciting a proportion, or treating it as a count and using > chi2) if you have sufficient sample sizes (see what happens when you compare > chi2 with t-test for proportions)... However, if you have a multiple > categorical variable, then I believe you'd need to create dummies for use in > -pbalchk- > > In any case, I can't really provide more guidance, since I not sure exactly > what is going on given the limited information you provided. > > Ariel * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Attachment:
pm26.log**

**References**:**re: Re: st: Standardized difference of means after PS matching***From:*"Ariel Linden. DrPH" <ariel.linden@gmail.com>

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