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

[José Maria Pacheco de Souza <jmpsouza@usp.br>]

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, among those 
at risk. In this case, aftward it will difficult to resist the temptation 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-intervention 
> ADOPT=NO crowd makes sense. I think you are also sneakily suggesting that 
> the most obvious null hypothesis -- "H0: p = 0" is not a good choice; 
> there would probably be some adoption even in the absence of the 
> intervention, and the intervention probably cannot be called a success 
> unless the proportion of adopters exceeds a minimum cost/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 null hypothesis 
> is useful. I think the following is more informative:
>
> Assume that you had 90 participants, 40 of whom already had the good 
> habit, leaving 50 "at risk" for improvement. 20 (40%) of these improved. 
> The 95% CI for this estimate is 26%-55%:
>
> . cii 50 20 , binomial
>                                                         -- Binomial 
> Exact --
>    Variable |        Obs        Mean    Std. Err.       [95% Conf. 
> Interval]
> -------------+---------------------------------------------------------------
>             |         50          .4     .069282        .2640784 
> .548206
>
> Hope this helps
> Svend

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