Tackling Hofstadter’s Law with confidence intervals

Hofstadter’s Law: It always takes longer than you expect, even when you take into account Hofstadter’s Law.

One of the frustrating things about developing software is that tasks always seem to take longer to complete than you expected before you started. Somehow, we’re always almost done on whatever feature we’re working on.

I’ve also long been a fan of the idea of using 90% confidence intervals instead of point estimates. Hubbard discusses this in his wonderful book How to measure anything. Instead of trying to pick how long a task will take (e.g., 4 days), you try to predict a range where you are 90% certain that the time will fall within that range (e.g., 3 – 15 days).

I’m going to put my money where my mouth is and try doing confidence interval estimates when working on a feature or bug. I ginned up a quick form using Google Forms and my aim is to fill it in each day, and then evaluate how well I can come up with 90% estimates.

Effort estimation

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