Hello everyone, I am trying to define a PERT distribution "by hand" by transforming a classic beta distribution - as I would like to understand where the shape parameter (default value of 4) comes from in the mc2d package. The help page says "The PERT distribution is a beta distribution extended to the domain [min, max] with mean mu = (min + shape * mode + max)/(shape + 2)" At the same time, we know that a 4 parameter beta distribution's mean can be expressed as mu = (alpha * max + beta * min)/(alpha + beta) So using the equality between the 2 expressions of mu I can find the shape parameter as a function of alpha and beta. But if I want to set the shape parameter to 4, how do I define alpha and beta? All I know is that my distribution is unimodal and positively skewed. In other words, is there a way to find the values of the 2 shape parameters of the "underlying beta distribution" by setting the min, max, mode, maybe some constraints on alpha and beta (alpha < beta; >1) and R-defined unique shape parameter? I think maybe I am missing something here. Many thanks ________________________________ This message and any attachments contain information that may be RMS Inc. confidential and/or privileged. If you are not the intended recipient (or authorized to receive for the intended recipient), and have received this message in error, any use, disclosure or distribution is strictly prohibited. If you have received this message in error, please notify the sender immediately by replying to the e-mail and permanently deleting the message from your computer and/or storage system. [[alternative HTML version deleted]]