## initial values for a proportional estimate

MDP
2013-05-09
2013-05-10

• MDP
2013-05-09

I am working through a basic problem from Kruschke's book in preparation to modify the code for my particular problem Specifically, I am trying to reproduce the binomial proportion example as follows:

Given 14 coin flips, 11 flips are "heads" or successful. Estimate the proportion of successes from the data below:

```coin_data <- c(r(1,11), r(0,3))
N <- length(coin_data)
binom_estimate <- "model{

for(i in 1:N){
y[i] ~ dbern(theta)
}
# Priors
theta ~ dbin(priorA, priorB)
priorA <- 1
priorB <- 1
}
"
writeLines(binom_estimate, con="binom_estimate.txt")
```

And, here is the implementation... cutting out some of the stuff Kruschke does for
simplification.

```# required packages
library(rjags)

# set up the bayesian estimate
data_list <- list(y = coin_data,
N = N)

# run the model
bayes_estimate <- jags.model("binom_estimate.txt",
data = data_list,
n.chains = 3,

update(bayes_estimate)

bayes_estimated_results <- coda.samples(bayes_estimate,
c("theta", "priorA", "priorB"),
n.iter=1000)

summary(bayes_estimated_results)
```

My result, with my current version of R2jags = 0.03-08 and JAGS = 3.3.0 is:

```Error in node y[12]
Observed node inconsistent with unobserved parents at initialization
```

If anyone has any suggestion on how I can fix this or how to provide useful initializations,
I would love to read them. I have read through the threads posted on this type of topic and
tried the solutions that seem to fit my particular problem, but haven't been able to get it
work.

Best,

MDP

• Martyn Plummer
2013-05-09

There are a couple of typos in your code. Firt, there is no `r` function in R, but there is a rep function, which I'm guessing is what you meant

Secondly, the line

```theta ~ dbin(priorA, priorB)
```

in your BUGS code should be replaced by

```theta ~ dbeta(priorA, priorB)
```

Then everything should work fine.

• MDP
2013-05-10

UGH!!!! I feel like such a heal...THANK YOU.