Try bpower or samplesize.bin in Hmisc package.

I do have a nonoficial function to estimate minimum smaple size for
comparison of two sensitivities or twu specificities. But it seems not to be
the case!

Abraço forte e que a força esteja com você,

Dr. Pedro Emmanuel A. A. do Brasil
Instituto de Pesquisa Clínica Evandro Chagas
Fundação Oswaldo Cruz
Rio de Janeiro - Brasil


2009/10/16 <r-sig-epi-request@stat.math.ethz.ch>

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>   1. Sample size for diagnostic test (Rahul Shidhaye)
>   2. R:  Sample size for diagnostic test (Guazzetti Stefano)
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> ----------------------------------------------------------------------
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> Message: 1
> Date: Thu, 15 Oct 2009 19:19:08 -0700 (PDT)
> From: Rahul Shidhaye <rahulshidhaye@yahoo.com>
> Subject: [R-sig-Epi] Sample size for diagnostic test
> To: r-sig-epi@stat.math.ethz.ch
> Message-ID: <5968.32620.qm@web53105.mail.re2.yahoo.com>
> Content-Type: text/plain
>
>
> Hello,
>
> I wish to calculate sample size for a disgnostic test. prevalence of the
> disorder is around 5% and expected sensitivity and specificity is 80%. We
> wish to have a precision of 5% in sensitivity and specificity.
>
> Dr. Rahul Shidhaye
>
>
>
>        [[alternative HTML version deleted]]
>
>
>
> ------------------------------
>
> Message: 2
> Date: Fri, 16 Oct 2009 11:05:31 +0200
> From: "Guazzetti Stefano" <Stefano.Guazzetti@ausl.re.it>
> Subject: [R-sig-Epi] R:  Sample size for diagnostic test
> To: "Rahul Shidhaye" <rahulshidhaye@yahoo.com>,
>        <r-sig-epi@stat.math.ethz.ch>
> Message-ID:
>        <EBE45F91B9606842A974F9F99E2D4E2B01BC8E9C@RE2-EXC-VBE1B.ausl.org>
> Content-Type: text/plain;charset=utf-8
>
> Dear Rahul,
> sensitivity and specificity are just proportion and thus it should not be
> hard
> to calculate the sample size needed in your case. Note also that
> sensitivity
> and specificity don't depend (at least in theory) on the prevalence of
> disease.
>
> RSiteSearch("proportion sample size")
>
> will suggest you more than one function to calculate the sample size for a
> single
> proportion under different assummptions.
> Under the assumption of independence and using the asymptotic ("normal")
> approximation
> you could use a simple function like this one:
>
> sampl.size.prop<-function (p, d, conf.lev=0.95, N=NULL){#N is for a finite
> population
>    if (any(c(d, p, conf.lev) > 1) || any(c(d, p, conf.lev, N) < 0))
>        stop("Error: proportions cannot exceed 1 or be negative")
>    z <- qnorm(1 - ((1 - conf.lev)/2))
>    n <- (z^2 * p * (1 - p))/d^2
>    if (is.null(N))
>        return(ceiling(n))
>    else return(ceiling(n/(1 + n/N))) }
>
> sampl.size.prop(0.8, 0.025)
> sampl.size.prop(0.8, 0.05)
> #not shure if you need a 5% coverage or plus/minus 5%
>
> Stefano
>
> -----Messaggio originale-----
> Da: r-sig-epi-bounces@stat.math.ethz.ch
> [mailto:r-sig-epi-bounces@stat.math.ethz.ch]Per conto di Rahul Shidhaye
> Inviato: Friday, October 16, 2009 4:19 AM
> A: r-sig-epi@stat.math.ethz.ch
> Oggetto: [R-sig-Epi] Sample size for diagnostic test
>
>
>
> Hello,
> ?
> I wish to calculate sample size for?a disgnostic test. prevalence of the
> disorder is around 5% and expected sensitivity and specificity is 80%. We
> wish to have a precision of 5% in sensitivity and specificity.
>
> Dr. Rahul Shidhaye
>
>
>
>        [[alternative HTML version deleted]]
>
>
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