Software Estimation Without Guessing

The Stochastic Model Approach

If a parametric model is too static, or you’d rather see the basis for the parametric coefficients in use, you can use a stochastic model. A stochastic model takes into account the random variations and gives you a probability distribution for an answer.

Perhaps you estimate (or assume a constant) the duration of each story, and then you model a random delta around that. Or you estimate the minimum duration of each story and model a random delay added to that. Either gives you a probability distribution for completion of that story. And if you add up the probability distributions for all the stories, you get a probability distribution for the release. In some environments, the contributions of delays swamp the amount ...