Lorin Hochstein

Ramblings about software, research and other things

Estimating confidence intervals, part 6

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Our series of effort-estimation-in-the-small continues. This feature took a while to complete (where “complete” means “deployed to production”). I thought this was the longest feature I’d worked on, but looking at the historical data, there was another feature that took even longer.


Somehow, the legend has disappeared from the plot. The solid line is my best estimate of time remaining each day, and the dashed line is the true amount of time left. The grey area is my 90% confidence interval estimate.


As usual, my “expected” estimate was much too optimistic. I initially estimated 10 days, where it actually took 17 days. I did stay within my 90% confidence interval, which gives me hope that I’m getting better at those intervals.

When I started this endeavor, my goal was to do a from-scratch estimate each day, but that proved to require too much mental effort, and I succumbed to the anchoring effect. Typically, I would just make an adjustment to the previous day’s estimate.

Interestingly, when I was asked in meetings how much time was left to complete this feature, I gave off-the-cuff (and, unsurprisingly, optimistic) answers instead of consulting my recorded estimates and giving the 90% interval.


Written by Lorin

September 20, 2014 at 11:55 pm

Posted in software

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