Part of a series on Making better estimates.
Mining data from prior projects, especially if time was formally tracked, can be an invaluable source of data for estimation efforts
Using data from prior projects is an easy way to ground your estimates in some reality. If you don’t track your time, and hence don’t have an accurate database from prior projects, shame on you. But don’t let that stop you. If you have to gather data from unreliable sources (people’s memories, for instance), then keep it coarse (weeks, not hours; months, not weeks).
If you made estimates on prior projects, and you have data about how long the projects actually took, use that comparison to reflect on how the estimate varied from the reality. Feed what you learn into your current estimation effort.
The task decomposition from prior projects is also a good place to check your current work against. If your projects are similar in nature you may eventually develop a check-list of items to be sure are on your estimation radar.
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