Estimates are not Law nor Fire and Forget
by: Jon M Quigley
There has been some twitter-go-round regarding estimates. Estimates are not always guesses, but very frequently these maybe just that. If we chose not to delude ourselves, we know when we have some substance behind our estimates, that is our estimates are based upon some relevant historical data that allows us to see the range of possibilities for this specific type of work as part of deriving the estimates. That is not to say that this is perfect only to say that there is some historical reason for our estimates, the further afield this specific work is from those earlier types of work, the more risk in the estimates.
In many cases estimates should not be point source estimates, that is a single number. This provides the illusion of certainty to those looking at the estimates. I think this is probably one of the reasons why managers and executives seem to treat these numbers as if these are very certain. The level of uncertainty is not articulated when using discrete single point estimates.
Estimates are not there only to establish the amount of time or cost for some set of activities but are also provide us some reference point from which we will compare the actual work. This allows us to adjust the estimates as we progress through the work which provides us with an up to date assessment of what the duration (time) or cost may be ultimately, as we progress through the project.
For things about which we know very little, we can still estimate using whatever mechanism we believe helps us, again estimates are not just to set an immovable business case or to Gantt chart, in fact that is exactly not at all what estimates should be in my humble opinion. Estimates are compared to the actual rate of accomplishment or expenditure and used to help predict the end result. We will use earned value management techniques to calculate what is likely to be the final cost, or date of conclusion for the task or indeed the project. I suggest checking out the Earned Value Management techniques to see how these things can work. I have reviewed the Wikipedia article and it essentially provides a fairly direct and easy to understand treatment of the EVM. It can be found at: https://en.wikipedia.org/wiki/Earned_value_management