R Function to Calculate Confidence Interval from Odds Ratio and P-value

Every once in a while I need a confidence interval from a published estimate that only reports the estimated odds ratio and respective p-value. With a little bit of algebra it is simple to build a function in R to calculate a confidence interval. Below is a short, easy example script.

	# Estimate CI from OR Estimate and P-value
	or <- 1.15
	p <- 5e-8
	# Program to calculate 95%CI
	calc_ci <- function(or, p, level=0.95)
	{
	b <- log(or)
	se_b <- b/qnorm(1-p/2)
	z <- qnorm(1-(1-level)/2)
	lci <- exp(b-z*se_b)
	uci <- exp(b+z*se_b)
	if (lci<uci)
	{ci <- c(lci,uci)}
	else
	{ci <- c(uci,lci)}
	return(ci)
	}
	calc_ci(or,p)

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