Estimates in everyday life

One thing that we teach in Agile courses is estimating. One technique is taken from Steve McConnell and called Count, Compute, and Judge. The idea is that, to make an estimate, you have 3 options. First, if you can Count, do so (ie. do not do any estimate at all). Second, take a value that you know, then count it, then Compute the resulting value to obtain the estimate. Finally, if all else fails, use your Judgment. It is a good idea to mix compute & judge.In two recent instances, I have heard outrageous figures when talking with friends. One mentioned that “the average pregnancy age is 13 years old”. In a separate discussion, another asserted that “the price of baguette has increased 6-fold since the introduction of the euro”.

Obviously, in the context of this post, it sounds trivial that these sentences are nonsense. However, in the heat of the conversation, they can pass unnoticed. Both persons seemed actually convinced that they were true, and used them as proof to further the debate.

How often are we taking random figures at face value? (“we have estimated this project to cost this much”) We should always be at least critical.
The idea is to think of other things to judge the figure against (“the laws of economics would probably prevent the price of bread to increase so fast in such a short time”). Intuition helps, naturally.

Common sense is the most fairly distributed thing in the world” (Descartes). It seems that it is still not enough. Let’s keep in mind that others can be wrong, and that we ourselves can be wrong. Judging people and behavior is foolish, but judging data is not.

So, when hearing figures, always keep a critical mind, especially if this figure is used to take decisions. Conversely, do not show figures as hard facts. Be as honest as possible and make clear that “well, I heard this on the radio, but I might have misunderstood”. Giving a wide range of possible values helps too (“the most probable estimate is 1000 man-days, but plausible estimates range from 500 to 5000”). You’ll be helping others, and yourselves.

About Eric Lefevre-Ardant

Independent technical consultant.
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