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From |
Antonio silva <asilva@inbox.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: logistic regression complex samples |

Date |
Thu, 8 Dec 2011 19:31:37 -0800 |

Dear Steve. It works now!.Thanks for all your help. And many thanks to everyone who helped me . Best regards, Antonio. > -----Original Message----- > From: sjsamuels@gmail.com > Sent: Thu, 8 Dec 2011 09:26:16 -0500 > To: statalist@hsphsun2.harvard.edu > Subject: Re: st: logistic regression complex samples > > Correction, the command for getting -svylogitgof- is "findit svylogitgof" > > Steve > > On Dec 7, 2011, at 10:43 PM, Steve Samuels wrote: > > > Thanks for the detailed command output, but you are on the wrong track. > The error message has nothing to do with leaving a cluster variable (PSU > or "primary sampling unit") out of the -svyset- command. SAS and Stata > behave the same in this regard. The proof is that in the -logistic- > results, the "Number of PSUs" and "Number of obs" are the same. > > We've already given you suggestions and links for fixing the problem > identified by the error message. There are different solutions, and you > will have to choose. You have encountered Stata's default behavior when > there is only one PSU in some strata. I suspect it's intended to force > the user to make a deliberate choice. > > The most conservative approach (biggest standard errors) would be the > following: > > ********************************************************************* > svyset [pweight= var_weight], strata(var_strata) singleunit(centered) > ********************************************************************* > > I suggest that you figure out why there are singleton strata, because the > answer might help you choose a better solution. One possibility is that > there were more observations in the stratum, but that all but one have > missing values for an analysis variable. Another guess is that you have > a subset of the original survey data, and the subgroup has only one > member in some strata. (If you have subset the data, you should use a > -subpop- option in your -svy: logistic- model.) Still another possibility > is that some observations were marked in advance to be in the sample; in > other words they are "certainty" units; and each was given its own > stratum. This is one of the possibilities for the -singleunit()- option > of the -svyset- command. > > The contributed command you refer to (the FAQ ask that you give exact > references) is -svylogitgof-. You can install it by typing "find > svylogitgof" and going to the first listed "package". > > > Steve > sjsamuels@gmail.com > > > > > > > > On Dec 7, 2011, at 8:01 PM, Antonio silva wrote: > > Thanks for the replies. I can run a model using SAS surveylogistic > without the cluster variable but I have had difficulties to do the same > with Stata version 11. I am a beginner in Stata programming.My final goal > is to calculate the Archer and Lemeshow (A-L; 2006) goodness of fit > test (with estat gof command) that is not available in SAS. To do that I > have to run correctly the logistic regression model (with only weight > and strata without cluster) in Stata. I hope someone can help with the > Stata code. > Consider the following code (ex. with 2 categorical covariates) that > have been used and the output . > > svyset [pweight= var_weight], strata(var_strata) > > > . xi: svy: logistic outcome i.covar1 i.covar2_3cat > > > i.covar1 _Icovar1_1-2 (naturally coded; _Icovar1_1 > omitted) > i.covar2_3cat _Icovar2_3_1-3 (naturally coded; _Icovar2_3_1 > omitted) > (running logistic on estimation sample) > > Survey: Logistic regression > > Number of strata = 9 Number of obs = > 398 > Number of PSUs = 398 Population size = > 4361.1088 > Design df = > 389 > F( 0, 389) = > . > Prob > F = > . > > ------------------------------------------------------------------------------ > | Linearized > outcome | Odds Ratio Std. Err. t P>|t| [95% Conf. > Interval] > -------------+---------------------------------------------------------------- > _Icovar1_2 | 1.926984 . . . . > . > _Icovar2_~2 | .2875105 . . . . > . > _Icovar2_~3 | .1978389 . . . . > . > ------------------------------------------------------------------------------ > Note: missing standard errors because of stratum with single sampling > unit. > > Thanks, > Antonio. >> -----Original Message----- >> From: skolenik@gmail.com >> Sent: Wed, 7 Dec 2011 11:18:37 -0600 >> To: statalist@hsphsun2.harvard.edu >> Subject: Re: st: logistic regression complex samples >> >> Antonio, >> >> it would help if you mentioned the version of Stata that you are >> using. By default, Stata would use observations as PSUs (and the >> output of -svyset- would state that -- again, it would help if you >> included the output of both commands). You can also achieve the effect >> of specifying observations as PSUs via -svyset _n ...-. >> >> On Wed, Dec 7, 2011 at 10:05 AM, Antonio silva <asilva@inbox.com> wrote: >>> Hello, >>> I would like to perform binary logistic regression in stratified >>> sampling incorporating 2 variables that represents that design >>> var_weight and var_strata. >>> Considering a model with 2 covariates , in SAS I would consider a code >>> like this that works perfectly: >>> >>> PROC SURVEYLOGISTIC DATA = dataset >>> STRATA var_strata; >>> >>> WEIGHT var_weight; >>> >>> >>> CLASS covariate1 >>> Covariate2 ; >>> >>> MODEL outcome(event='1')= covariate1 covariate2 /clparm vadjust=none ; >>> Run; >>> >>> >>> I tried an equivalent Stata code but does not work. It seems that in >>> Stata its is always necessary have the cluster variable. But in my >>> design I do not have cluster variable,only weight and strata. >>> >>> svyset [pweight= var_weight], strata(var_strata) >>> >>> svy: logistic outcome i.covariate1 i.covariate2 >>> >>> After run , in the output appears only the OR calculated and a note: >>> Note: missing standard errors because of stratum with single sampling >>> unit. >>> What is wrong with it? >>> >>> After that I did some tests considering a fictitious cluster variable >>> and worked. I suppose this command works only when the 3 design >>> variables weight strata and cluster are used at the same time. >> >> -- >> Stas Kolenikov, also found at http://stas.kolenikov.name >> Small print: I use this email account for mailing lists only. >> >> * >> * 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/ > > ____________________________________________________________ > Share photos & screenshots in seconds... > TRY FREE IM TOOLPACK at http://www.imtoolpack.com/default.aspx?rc=if1 > Works in all emails, instant messengers, blogs, forums and social > networks. > > > > * > * 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/ > > > > * > * 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/ ____________________________________________________________ Send any screenshot to your friends in seconds... 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**References**:**Re: st: logistic regression complex samples***From:*Steve Samuels <sjsamuels@gmail.com>

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