Pick the mean (mu) and variance (sig2) you want. Then, shape = mu^2/sig2 and scale = sig2/mu. This should work fine if your mean is large enough so that p(x = 0 or 1) is small. -- View this message in context: http://r.789695.n4.nabble.com/Gamma-count-tp4711845p4711853.html Sent from the R help mailing list archive at Nabble.com.