Estimating tasks with points

September 17, 2008

Following on from my entry on the altnetuk session on Agile Process, I’m just going to layout the different types of estimating with points that I know of. I’m not sure why but at that session it felt like someone had put and end to point to complexity estimating and forgot to let me know!

Pure time based estimates

You’ll be wrong. The time it takes for dev a to do a task will be different to the time it takes dev b. You will run in to problems with the task and it’ll totally throw all your estimates out (may be exaggerating).

Your manager will not understand why you can’t do 7.5 hours worth of work in a day. There is no room for ramp up, context switching or any of those minutes you don’t think of.

Burn down charts tend also to look like complete failures. As every hour of your day is accounted for, but you don’t actually spend every hour of our day on storied tasks, those other hours show up on a burn-down chart as slacking. When this happens, it’s not reasonable for the team to commit to less in the next iteration, as it implies they’re not spending their time doing any work. This totally ruins the point of committing to any work in a planning meeting, if there is little or no intention of completing it all. This also makes it difficult to ball park future iterations.

Time to points

The team eventually manages to estimate tasks without thinking about the time it takes. Easy to figure out your capacity or velocity. Easy to manage when team size fluctuates (illness, holiday, expansion). Easier to sell to management. No room for improvement, how do you increase our velocity without making time? It’s possible, but only by admitting that you’re not estimating with time any more.

Pure points

Difficult to start a project with a new team. I do this by assuming we’re unstoppable and committing to all the stories we have. Then I use the number of points we do complete as a baseline for the following iterations. Motivates developers quickly. Increasing velocity in this way is far easier to motivate developers with. The idea that you’re getting better at doing work is much nicer than the idea that your old estimates were slack. More quickly with pure points do new developers fall into line in planning poker. They stop influencing the task with how quick they think they are (maybe quicker than some of the team maybe slower) and go straight to how complicated the task is. Points always help when you get estimating discrepancies. More clearly separates your teams estimating technique / accuracy from another’s. With a per team velocity and meaning for points, it’s more difficult for management to unfairly compare two teams estimates and use it as a flawed performance indicator.

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