## Bernoulli model, Normal prior"
normal_prior <-
function(p = 0.3, n = 10, mu = 0, var = 1, scale = c("prob", "logit"), seed = 0)
{
scale <- match.arg(scale)
if (p < 0 || p > 1)
stop("p must be in 0-1")
if (n < 1 || n > 1000)
stop("n must be on 1-1000")
set.seed(seed)
y <- rbinom(n = 1000, size = 1, p = p)
pval <- seq(0.001, 0.999, by = 0.0005)
fLik <- function(p, y)
prod(dbinom(y, size = 1, prob = p))
fPri <- function(p, mu, var, scale) {
if (scale == "prob")
out <- (1/(p*(1-p))) * dnorm(qlogis(p), mu, sqrt(var))
if (scale == "logit")
out <- dnorm(qlogis(p), mu, sqrt(var))
out
}
Lik <- sapply(pval, fLik, y=y[1:n])
Pri <- sapply(pval, fPri, mu, var, scale)
Pos <- Lik * Pri
M <- cbind(Pri=Pri/max(Pri),
Lik=Lik/max(Lik),
Pos=Pos/max(Pos))
if (scale == "logit") {
p <- qlogis(p)
pval <- qlogis(pval)
} else {
p <- p
}
Col <- c("#cccccc", "#3498db", "#f39c12")
op <- par(las = 1)
matplot(pval, M, type = "l",
col=Col, lwd=2, lty=1,
ylab = "Density",
xlab=ifelse(scale == "logit", "logit(p)","p"),
sub=paste0("Mean = ", round(mean(y[1:n]), 2), " (",
sum(1-y[1:n]), " 0s & ", sum(y[1:n]), " 1s)"),
main = paste0("True value = ", round(p, 2),
", Posterior mode = ", round(pval[which.max(Pos)], 2)))
abline(v = p, lwd = 2, col = "#c7254e")
abline(v = pval[which.max(Pos)], lwd = 2, col = "#18bc9c")
legend("topleft",lty=1, lwd=2, col=Col, bty="n",
legend=c("Prior","Likelihood","Posterior"))
par(op)
if (scale == "prob") {
M <- cbind(p=pval, M)
} else {
M <- cbind(logit_p=pval, M)
}
invisible(data.frame(M))
}
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