This model is a very common approach – the person putting together the cost estimations collects information from experts in the areas of the new requirements. The experts use their knowledge, experience, and their own techniques to provide a cost estimate.
This model feels safer and more precise, as someone with experience is providing the numbers. It provides an accurate result in most cases. It is an especially effective approach to delivering estimations when combined with one or more of the other techniques in this blog.
This method probably takes the longest, as you have to wait to receive the feedback from the experts. It’s not bullet-proof either – statistically, the accuracy of this approach decreases as the size of the requirements in question increases, so it’s not a scalable model.