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From |
"Michael I. Lichter" <mlichter@buffalo.edu> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Re: single sample pre/post comparison of proportions |

Date |
Thu, 11 Jun 2009 13:10:55 -0400 |

Thanks to both of you for your suggestions. Michael José Maria Pacheco de Souza wrote:

bound p(known), test a hypothesis Ha: p(new)>p(known) vs H0:p(new)=p(known), using the at risk of improving.Or as Svend presented, just estimate the proportion of new, amongthose at risk. In this case, aftward it will difficult to resist thetemptation to compare this result with the p(known).Cheers, José Maria Jose Maria Pacheco de Souza, Professor Titular (aposentado) Departamento de Epidemiologia/Faculdade de Saude Publica, USP Av. Dr. Arnaldo, 715 01246-904 - S. Paulo/SP - Brasil fones (11)3061-7747; (11)3768-8612;(11)3714-2403 www.fsp.usp.br/~jmpsouza -----Michael asked and Joseph responded (not shown) - and Michael then wrote:The suggestion of a one-sample test restricted to pre-interventionADOPT=NO crowd makes sense. I think you are also sneakily suggestingthat the most obvious null hypothesis -- "H0: p = 0" is not a goodchoice; there would probably be some adoption even in the absence ofthe intervention, and the intervention probably cannot be called asuccess unless the proportion of adopters exceeds a minimumcost/benefit threshold. Instead, I could choose, e.g., "H0: p < .25"(a one-tailed test). That seems reasonable.===============================================================I wonder whether a P-value related to a somewhat arbitrary nullhypothesis is useful. I think the following is more informative:Assume that you had 90 participants, 40 of whom already had the goodhabit, leaving 50 "at risk" for improvement. 20 (40%) of theseimproved. The 95% CI for this estimate is 26%-55%:. cii 50 20 , binomial-- BinomialExact --Variable | Obs Mean Std. Err. [95% Conf.Interval]-------------+---------------------------------------------------------------| 50 .4 .069282 .2640784 .548206 Hope this helps Svend* * 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/

-- Michael I. Lichter, Ph.D. <mlichter@buffalo.edu> Research Assistant Professor & NRSA Fellow UB Department of Family Medicine / Primary Care Research Institute UB Clinical Center, 462 Grider Street, Buffalo, NY 14215 Office: CC 125 / Phone: 716-898-4751 / FAX: 716-898-3536 * * 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/

**Follow-Ups**:**Re: st: Re: single sample pre/post comparison of proportions***From:*José Maria Pacheco de Souza <jmpsouza@usp.br>

**References**:**Re: st: Re: single sample pre/post comparison of proportions***From:*Svend Juul <SJ@SOCI.AU.DK>

**Re: st: Re: single sample pre/post comparison of proportions***From:*José Maria Pacheco de Souza <jmpsouza@usp.br>

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