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From |
Steven Samuels <sjhsamuels@earthlink.net> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: trend analysis for survey data |

Date |
Mon, 10 Mar 2008 15:03:26 -0400 |

The mean of a binary variable is the proportion with the event. Thus - svy regression- will give a test for trend in proportions. For proportions between 20% and 80%, linear, logit, and probit transformations have similar fits (DR Cox, Analysis of Binary Data, Methuen 1970). The 'Chi Square Test for Trend in Proportions' for independent, non-survey data (e.g. PA Armitage Statistical Methods in Medical Research,Wiley, 1971, p 363) is essentially a test for a non- zero linear regression coefficient for proportions under the null hypothesis. (Moreover, it is the maximum likelihood score test for trend in logistic regression (reference: I forget).) All in all the linear version is much easier to interpret. Either the linear or logistic version have the proper type 1 error rate, but Audrey should decide which scale to use after plotting her data. Certainly if she wants to interpolate, extrapolate, or summarize the prediction with a regression coefficient, she should choose a well-fitting model.

-Steven

On Mar 10, 2008, at 2:35 PM, Mohammed El Faramawi wrote:

Hi steven, It seems that I am missing something. Why do you recommend using svy:regress with a categorical variable?? why not svy:logit from the beginning? thank oyu --- Steven Samuels <samplerx@earthlink.net> wrote:-svyset- your data. Then try -svy reg- for your 0-1 outcome on the time dimension variable. If the prevalences are close to zero or one, you could consider -svy logit -. From your question, I take it that the surveys are independent, but taken over the time dimension and that the target populations were identical, except for time period. You will need to define new strata, which are combinations of survey and the original strata. This assumes that primary sampling units were newly sampled for each survey. If not, you cannot treat the surveys as independent and should come back here for help. -Steven On Mar 10, 2008, at 4:28 AM, audreyp@neo013.net wrote:hi, I have data on three/four independentcross-sectional surveys (notpanels). I need to test for a trend in theprevalence of a healthcondition. How can I do a trend analysis in Statathat will takeinto account sampling weights and stratification? thank you. Audrey P. * * For searches and help try: *http://www.stata.com/support/faqs/res/findit.html* http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/Steven Samuels 845-246-0774 18 Cantine's Island Saugerties, NY 12477 EFax: 208-498-7441 * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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**References**:**Re: st: trend analysis for survey data***From:*Mohammed El Faramawi <melfaram@yahoo.com>

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