Over the last few months I've been thinking about how people perform estimates when developing software. I've take time - not enough - to look through some of the research on estimation and try and understand how we can improve estimates.
I’ve written a long (11 pages, over 6000 words), and rough, essay recording some of my findings. You can download “Estimation and Retrospective Estimation” from my website, I don’t intend to publish the essay anywhere but I expect some of the findings to be included in some future pieces. In this blog entry and the next I want to report some of the motivation and findings.
To start, a correction and an apology.
In January Jon Jagger sat in on one of my Agile training courses. Jon asked me about two references I appeared to cite. I have failed to be able to support these references with the necessary research and I must apologise to Jon and others who heard me say I could.
Now if someone, me or anyone else, goes around saying “there is evidence for this” or “this is backed by research’ they should be able to back it up. I have failed on this count. I apologise to Jon and everyone else who has heard me say these things. I can't track down my references. I should not have claimed there is research which I can't provide a reference for.
I’m going to repeat my claims now for two reasons. First, I’m hoping that someone out there will be able to point me at the information. Second, if you’ve heard me say either of these things and claim there is research to back it up then, well I apologise to you too. And if you hear anyone else say similar things, please pin them down and find the original source.
The first thing Jon pulled me up on was in the context of planning poker. I normally introduce this as part of one of my course exercises. Jon heard me say “Make your estimates fast, there is evidence that estimates fast estimates are just as accurate as slow ones.”
Does anyone have any references for this?
I still believe this statement, however, I can’t find any references to it. I thought I had read it in several places but I can’t track them down now. I’m sorry.
Thinking about it now, I think I originally heard another Agile trainer say this during a game a planning poker a few years ago. So its possible that others have heard this statement and someone has the evidence.
Turning to my second dubious claim, I said: “I once saw some research that suggests we are up to 140% in judging actuals.” It is true that I read some research that appeared to show this - I think it was in 2003. However, I can’t find that research so I can’t validate my memory, therefore this is not really valid.
By "actuals" I mean: the actual amount of time it took to do a piece of work.
Again, does anyone know the research I have lost the reference to?
And again, I apologise to Jon and everyone who has heard me state this as fact. It may well be true but I can't prove it and should not have cited it.
Why did I say it? Well, I find a lot of people get really concerned about the difference between estimates and actual, whether some task was completed in the time estimated. To my mind this is a red herring, actuals only get in the way.
This is where things start to get interesting. I decided to look again at the research on estimation and specifically recording “actuals.” The first thing I learned was that what we call “actuals” is better called “retrospective estimation.”
The “Estimation and Retrospective Estimation” essay record my journey and findings in full. In my next blog entry I’m record some of my conclusions.