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From |
José Maria Pacheco de Souza <jmpsouza@usp.br> |

To |
<statalist@hsphsun2.harvard.edu> |

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

Date |
Thu, 11 Jun 2009 09:03:15 -0300 |

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 suggesting thatthe most obvious null hypothesis -- "H0: p = 0" is not a good choice;there would probably be some adoption even in the absence of theintervention, and the intervention probably cannot be called a successunless the proportion of adopters exceeds a minimum cost/benefitthreshold. Instead, I could choose, e.g., "H0: p < .25" (a one-tailedtest). That seems reasonable.===============================================================I wonder whether a P-value related to a somewhat arbitrary null hypothesisis 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 these improved.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 .2640784.548206Hope this helps Svend

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**Follow-Ups**:**Re: st: Re: single sample pre/post comparison of proportions***From:*"Michael I. Lichter" <mlichter@buffalo.edu>

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

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