Lorin Hochstein

Ramblings about software, research and other things

Estimating confidence intervals, part 2

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Here is another data point from my attempt to estimate 90% confidence intervals. This plot shows my daily estimates for completing a feature I was working on.

90% confidence intervals


The dashed line is the “truth”: it’s what my estimate would have been if I had estimated perfectly each day. The shaded region represents my 90% confidence estimate: I was 90% confident that the amount of time left fell into that region. The solid line is the traditional pointwise effort estimate: it was my best guess as to how many days I had left before the feature would be complete.

For this feature, I significantly underestimated the effort required to complete it. For the first four days, my estimates were so off that my 90% confidence interval didn’t include the true completion time: it was only correct 60% of the time.

This plot shows the error in my estimates for each day:


Error in effort estimate

Apparently, I’m not yet a well-calibrated estimator. Hopefully, that will improve with further estimates.


Written by Lorin

May 29, 2014 at 8:51 pm

Posted in research, software

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  1. […] episode in our continuing series of effort estimation in the small with 90% confidence intervals. I recently finished implementing […]

  2. […] the latest installment in my continuing saga to estimate effort with 90% confidence intervals. Here’s the […]

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