I’m of the opinion that estimating is more of a gift – you either have it or you don’t. It’s that ability to think somewhat abstractly on given tasks and figure out with some degree of accuracy what the level of effort will be. Of course, there needs to be a certain level of experience and expertise – but that experience does not always ensure that you’ll give good estimates. Over time, one can learn to be a good estimator, but it helps to have that gift.
With all that said, there are many things that can undermine the accuracy or validity of your estimates. Some you have control over and many that you can’t really control. Here are nine common pitfalls that can often negatively impact project estimates:
Poorly defined scope of work. This can occur when the work is not broken down far enough or individual elements of work are misinterpreted.
Omissions. Simply put, you forget something.
Rampant optimism. This is the rose-colored glasses syndrome, when the all-success scenario is used as the basis for the estimate.
Padding. This is when the estimator (in this case almost always the task performer) includes a factor of safety without your knowledge, a cushion that ensures that he or she will meet or beat the estimate.
Failure to assess risk and uncertainty. Neglecting or ignoring risk and uncertainty can result in estimates that are unrealistic.
Time pressure. If someone comes up to you and says, “Give me a ballpark figure by the end of the day” and “Don’t worry, I won’t hold you to it,” look out! This almost always spells trouble.
The task performer and the estimator are at two different skill levels. Since people work at different levels of efficiency, sometimes affecting time and cost for a task significantly, try to take into consideration who’s going to do the work.
External pressure. Many project managers are given specific targets of cost, schedule, quality, or performance (and often more than one!). If you’re asked to meet unrealistic targets, you may not be able to fight it, but you should communicate what you believe is reasonably achievable.
Failure to involve task performers. It’s ironic: an estimate developed without involving the task performer could be quite accurate, but that person may not feel compelled to meet the estimate, since “it’s your number, not mine,” so the estimate may appear wrong.
This article is based in part on information from Gary Heerken’s book “Project Management.”
I originally wrote this article for the PM Tips website. The original post appears here.