Problem: There is a huge difference between a guesstimate and an estimate.
Since both methods are measured in same variable they can look very similar. They both give some quantitative measures assigned to time or cost, but they differ greatly in in uncertainty.
Solution: Make sure that you ask the right question when requesting an estimate.
Wikipedia says it all about guesstimates: ”It is defined as an estimate made without using adequate or complete information, or, more strongly, as an estimate arrived at by guesswork or conjecture.”
It seems however that some people forgets that estimates are not certain, but over and over again both guesstimates and estimates ends up being the foundation of planning.
From a planning perspective estimates are necessary in order to make the plan, but it does not mean that the estimate cannot be checked. Even estimates from subject matter experts can be challenged by asking the right questions.
- What is the data and conditions used for the estimate?
- What does the estimate cover and what is the scope?
- What estimation methodology was applied?
- Are there any obvious uncertainties?
Data and conditions are important as understanding the estimate parameters and requirements is needed in order to check an estimate. These conditions provide the framework for the estimate and are what the estimate is compared against.
Coverage and scope indicates all the activities that are included, and maybe more important those that are not included in the estimate. The discussion on what is out of scope is healthy in the way that it aligns expectations and understanding of the tasks related to the estimate.
Estimation methodology says a lot about the certainty in the estimate. Applying FIA (finger in air) is often less accurate than planning poker in the development team. Check Wikipedia or other source for more info on the methodologies.
Uncertainties often comes from assumptions or dependencies – Look for those in the discussion and you are likely to uncover the uncertainties while doing so.
Note: this is not an invitation to question every estimate you come across, but a suggestion on how to increase accuracy of those estimates that are on your project’s critical path. Many an estimate you come across is in fact a guesstimates, challenging it might make it an estimate, reducing risk and improving accuracy of the planning in your project.
Happy estimating & have a nice weekend!