[R] Bayesian Credible Intervals for a Proportion

[Greg Snow]

It would help us to help you if you told us which package ncredint is in (it is not in any of the packages that is installed on the computer I am presently using, but could be in multiple others).

Does this interval match what you are expecting?

> library(TeachingDemos)
> hpd(qbeta, shape1=4, shape2=8)
[1] 0.09337233 0.58795256



-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of tinazilla
Sent: Wednesday, June 15, 2011 6:42 PM
To: r-help at r-project.org
Subject: [R] Bayesian Credible Intervals for a Proportion

I am trying to calculate Bayesian Credible Intervals for a proportion
(disease prevalence values to be more specific) and am having trouble using
R to do this. I am working with ncredint() function but have not had success
with it. Please help!

Example: 
Positive samples = 3
Total sampled = 10
Prevalence = 0.3

pvec <- seq(1,10,by=1)
npost = dbinom(pvec,10,prob=0.3, log=FALSE)
ncredint(pvec, npost, tol=0.01, verbose=FALSE)

But I don't get the right Bayesian CI. What am I doing wrong?

Thanks!
Tina

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