Estimating Project Delivery Time

I have spent a lot of my working life doing IT Project Estimation and IT Project Proposals, it is not the most interesting subject in the world, but it is important, and I touched upon it in an earlier post.

I could throw in a few key words used to manage the estimation, words like originality, uncertainty, statistics, experience, reductionism, but it would need thick volumes to explain them properly. What is interesting is why people keep getting their estimates wrong.

It is obvious that people tend to over-estimate their own abilities. That is such basic human nature and so well-documented that we may as well just call it fact.

But many people, even educated ones, seem to have trouble with simple extrapolation, even for things as commonplace as car journeys. The British Psychology Society just published a simple study that asked:

for both pairs, just make an intuitive judgement about which jump in speed will make the largest difference to your time of arrival (i.e. save the most time):

a)Travelling at 50km/h instead of 40km/h.
b)Travelling at 130km/h instead of 80km/h.

a)Travelling at 50km/h instead of 30km/h.
b)Travelling at 130km/h instead of 60km/h.

If you're like most of the participants in Svenson's study, you will have assumed that option (b) in both pairs is the most time saving.

That guess is simply wrong. In each case, option (a) saves more time. However far the journey.