Software Estimation Without Guessing

Decomposition Gotchas

The law of large numbers says that random errors tend to cancel each other out. Beware, however, of errors that are not random. If the errors are an integral part about how you’re doing the work, they are more likely to reinforce each other than to cancel out. If you’re adding up a large number of small estimates and the errors all tend in the same direction, the resulting error will be large. This can catch you by surprise if you don’t consider the systematic errors that may exist in your estimation process.

Here are some common causes of accumulating errors. Watch out for them. As the proverbial “they” say, “forewarned is forearmed.”

Making Consistent Size Errors

You may consistently imagine the pieces as larger or smaller ...