It’s interesting how the word estimate gets thrown around.
Different people seem to use the word in different ways – and do different things with the figures. John Rusk (from www.agilekiwi.com) and I have come to the conclusion that there are at least three different definitions:
Prediction – how long you expect the task to take.
Target – a goal for how long you would like to take.
Commitment – what you publicly agree to.
Ideally, your prediction should be based on the best available information, and should only reflect the effort required to get the task complete. Note that political and budgetary considerations shouldn’t impact on your prediction - but they can pay a part in deciding your target and your commitment.
With these definitions, we can make some interesting observations.
… if your target is less than your prediction, then you’re hoping to get things done more quickly.
… if your commitment is less than your prediction, then you’re planning to fail – or to lose money.