Lorin Hochstein

Ramblings about software, research and other things

Archive for April 2014

Results from estimating confidence intervals

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A few weeks ago, I decided to estimate 90% confidence intervals for each day that I worked on developing a feature.

Here are some results over 10 days from when I started estimating until when the feature was deployed into production.

Effort estimates

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.

If we subtract out the “truth” from the other lines, we can see the error in my estimate for each day:

Error in estimate

Some observations:

  • The 90% confidence interval always included the true value, which gives me hope that this an effective estimation approach.
  • My pointwise estimate underestimated the true time remaining for 9 out of 10 days.
  • My first pointwise estimate started off by a factor of two (estimate of 5 days versus an actual of 10 days), and got steadily better over time.

I generated these plots using IPython and the ggplot library. You can see my IPython notebook on my website with details on how these plots were made.


Written by Lorin

April 9, 2014 at 10:19 pm

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Happier developers are more productive

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I reviewed a paper for It Will Never Work In Theory. I’d cross-post it here, but Google apparently doesn’t like it when the same content appears on multiple sites.

Written by Lorin

April 1, 2014 at 1:26 pm

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