[R] loop troubles

[David Winsemius]

On Jul 17, 2010, at 9:09 PM, Joe P King wrote:

> Hi all, I appreciate the help this list has given me before. I have a
> question which has been perplexing me. I have been working on doing a
> Bayesian calculating inserting studies sequentially after using a
> non-informative prior to get a meta-analysis type result. I created a
> function using three iterations of this, my code is below. I insert  
> prior
> mean and precision (I add precision manually because I want it to be  
> zero
> but if I include zero as prior variance I get an error cant divide  
> by zero.
> Now my question is instead of having the three iterations below, is  
> there
> anyway to create a loop, the only problem is I want to have elements  
> from
> the previous posterior to be the new prior and now I cant figure out  
> how to
> do the code below in a loop.

Perhaps if you set the problem up with vectors, it would become more  
obvious how to do it with indexing or loops:

n <-  c(5, 10, 15)
ybar <- c(12,12,14)  # and so on...

-- 
David
> The data below is dummy data, I used a starting
> mu of 1, and starting precision of 0.
>
>
>
> bayes.analysis.treat<-function(mu0,p0){
>
> n1 = 5
>
> n2 = 10
>
> n3 = 15
>
> ybar1 = 12
>
> ybar2 = 13
>
> ybar3 = 14
>
> sd1 = 2
>
> sd2 = 3
>
> sd3 = 4
>
> #posterior 1
>
> var1 = sd1^2 #sample variance
>
> p1 = n1/var1 #sample precision
>
> p1n = p0+p1
>
> mu1 = ((p0)/(p1n)*mu0)+((p1)/(p1n))*ybar1
>
> sigma1 = 1/sqrt(p1n)
>
> #posterior 2
>
> var2 = sd2^2 #sample variance
>
> p2 = n2/var2 #sample precision
>
> p2n = p1n+p2
>
> mu2 = ((p1n)/(p2n)*mu1)+((p2)/(p2n))*ybar2
>
> sigma2 = 1/sqrt(p2n)
>
> #posterior 3
>
> var3 = sd3^2 #sample variance
>
> p3 = n3/var3 #sample precision
>
> p3n = p2n+p3
>
> mu3 = ((p2n)/(p3n)*mu2)+((p3)/(p3n))*ybar3
>
> sigma3 = 1/sqrt(p3n)
>
> posterior<-cbind(rbind(mu1,mu2,mu3),rbind(sigma1,sigma2,sigma3))
>
> rownames(posterior)<-c("Posterior 1", "Posterior 2", "Posterior 3")
>
> colnames(posterior)<-c("Mu", "SD")
>
> return(posterior)}
>
>
>
> -------------------------------------------
>
> Joe King, M.A.
>
> Ph.D. Student
>
> University of Washington - Seattle
>
> 206-913-2912
>
> <mailto:jp at joepking.com> jp at joepking.com
>
> -------------------------------------------
>
> "Never throughout history has a man who lived a life of ease left a  
> name
> worth remembering." --Theodore Roosevelt
>
>
>
>
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>
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David Winsemius, MD
West Hartford, CT