How Expectations Mess Up Project Estimates

Filed under Estimation | Posted by PMStudent

Glen Alleman recently pointed me to a paper by Jorge Aranda among other material on software estimation.

I sat down and read Anchoring and Adjustment in Software Estimation and it was well worth my time.

by Andrew Stawarz via Flickr

by Andrew Stawarz via Flickr

To cut to the chase, the subjects were tasked to give estimates for software tasks in a controlled manner, in 3 groups with various “anchoring” methods being used.? The only difference between the groups was the expectation statement by the manager before estimation.

Group 1 (control – no explicit anchor given)

?I?d like to give an estimate for this project myself, but I admit I have no
experience estimating. We?ll wait for your calculations for an estimate.?

Group 2 ( ‘2 months’ condition)

?I admit I have no experience with software projects, but I guess this
will take about 2 months to finish. I may be wrong of course, we?ll
wait for your calculations for a better estimate.?

Group 3 (’20 months’ condition)

?I admit I have no experience with software projects, but I guess this
will take about 20 months to finish. I may be wrong of course, we?ll
wait for your calculations for a better estimate.?

You will need to read the full paper to see all the goodies (and to determine if you think it is relevant to your domain), but I would like to summarize some of the results I found striking.

These were the results among all participants, and there are other slices of the data available in the paper including only experienced participants and also by estimation method chosen.

‘2 months’ condition

  • mean – 6.8 months
  • median – 6 months
  • standard deviation – 3.7

control – no explicit anchoring

  • mean – 8.3
  • median – 7
  • standard deviation – 4.4

’20 month’ condition

  • mean – 17.4
  • median – 16
  • standard deviation – 5.6

The results in general coincide with my own experience on this matter.? An important point to note is that even though they were supposedly estimating the exact same software requirements, it is very likely that the ‘2 month’ group would have produced a significantly different product than the ’20 month’ group.

Food for thought.

When you and your team are putting together estimates, what influences are creating these anchors?? From my experience there are many of them, some of which are likely to be arbitrary or set (even inadvertently) without sufficient knowledge or experience.? They may be coming from stakeholders, sponsors, the project manager, or even a team member/lead.

My favorite example of this is when a team is asked to provide a “back of the envelope” estimate without really understanding the scope yet.? It produces a bad estimate and sets a rather arbitrary anchor for future estimates.

What do you think?

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