Evaluating project completion times when activity times are Erlang distributed

One aspect of project planning risk assessment is to do with the uncertainty of the project duration. This uncertainty can be quantfied by determining the project completion time distribution. A brief review of the existing literature on project duration risk assessment methodologies is given and their advantages and disadvantages evaluated. A development of the moments method based on Erlang distribution of activity times provides an accurate estimate of a project completion time distribution for a large range of practical situations and also is the basis upon which multi-modal input distributions of activity times can be handled. The method is assessed by a number of illustrative examples.