simple Bayesian version of R's prop.test
Bayesian Test of the Difference Between Proportions
Provides a simple way to perform a Bayesian version of
prop.test using the beta distribution.
The default prior distributional parameters are a = 1 and b = 1. The prior can be adjusted if you have reasonable information to work with. If you set a < b, the density will be weighted toward the lower half of the distribution, and setting a > b would weight it toward the upper half. If a = 0.5, much more weight is given to values near 0, while if b = 0.5, weight is stacked up near 1. Examples of different shapes of the beta distribution based on different parameter values can be seen at Rocscience.
A histogram is produced of the posterior distribution, with a red reference line marking "no difference."
bayes.prop.test(n1, d1, n2, d2, a=1, b=1, rep=10000)
n1 The numerator of the first group. Required.
d1 The denominator of the first group. Required. The
proportion n1/d1 should be greater than or equal to n2/d2.
d2 The denominator of the second group. Required. The
proportion n2/d2 should be less than or equal to n1/d1.
a Alpha prior parameter. Defaults to 1.
b Beta prior parameter. Defaults to 1.
rep Number of replications for the
rbeta function. Defaults to 10,000.
bayes.prop.test(n1=50, d1=100, n2=20, d2=50)