Estimating stories – How accurate can we be?

So i recently attended a skills matter conference by Linda Rising about estimating stories and how realistically we can be in estimating the size of them which was a real eye opener. A large chunk of it was focused of how our brains actually work and therefore influence how we estimate a chunk of work.The first major point that was made is that we lie to other people and ourselves all the time. This is not just regarding stories, but everything!  We tend to have a rose-tinted view of the world which we means that not only are we over optimistic about our abilities but also the abilities of others. This over optimism then unconsciously gets translated into our estimates. Comments like “oh that’s just a link on a page, that’ll be easy” and “oh we’ve done that before so it’ll be easier this time around” are common place in estimation sessions.

To set the scene of the next point I’ll talk about how people can estimate story sizes. So we use story points of 1,2,4,8. Other companies i know use Fibonacci (1,2,3,5 etc) or “small”, “medium” or “large”. So the next problem is that your imaginary number/size which is relative to other stories of similar size will then have mathematical functions performed on it (e.g. division, subtraction etc) which on an imaginary number, doesn’t hold much value. E.g. you estimate a story as a 4, it then may get split into 2 ‘equal’ stories of 2. Math operations such as this don’t work with an imaginary number created by an unconsciously over-optimistic estimator.

So before you start throwing estimation out of the window there is some hope! The first key point is that do not try to estimate too much, too far in  advance. The result will be inaccurate at best. You’re better off estimating on things you are working on right now, not 6 months down the line. The reason for this is that as you’re working on the story you’re gradually reducing the amount of ‘unknown’ elements to it which means you have a better idea of what work could be still outstanding. The next point to be made is that continually review your estimates as you’re working through the story. Estimates should be a continuous feedback loop to project managers to indicate if your story is on track or spiraling out of control and once your story has been completed, compare it with other stories which had the same estimate.

So to summarize:

  • As humans, we are over-optimistic liars to ourselves so PM’s add a bit of a buffer to the figure we come up with in estimates
  • Don’t estimate too much, too far in advance
  • Continuously review your estimates as you play the story

for those further interested in this topic, here’s the pod-cast: estimation & deception

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