We have started using Agile/Scrum in a team of 4 developers. We did our story estimations and ordered the stories Primed stories in the product backlog.
We started with the point based estimation on the complexity from 1 to 5, instead of usual 1,2,3,5,8,13…. and so on
After working on a couple of the stories we felt that some of the stories that was estimated at 4 point should only be 2 while the other which were estimated at 2 are a lot more complex and should have been estimated as 5. I would like to know:
- Is it Ok to change our story estimates in the middle of the iteration?
- Is it Ok to use the current estimation points from 1 to 5, instead of usual 1,2,3,5,8,13…. and so on
Although I personally feel that it should be no for both the cases but I need to back myself up as my own understanding is not very clear.(Any good ref material would be good though!)
Best Answer
Absolutely not. We expect that to happen. And we expect the errors to balance themselves out over time. We only really adjust estimates where it is clear that a certain category (e.g. new web pages) is always going to be more complex than we had thought when we estimated them all.
As an Epic story is broken down into smaller stories (which should happen long before the sprint), we might appear to adjust the original estimate, but I would call it refining rather than reestimating. That's because we have a clearer view at that time.
Mike Cohn's Agile Estimating and Planning is a good book on the subject. I would warn against using it (or any "Agile" book) as a bible, but it's a good start point from which to refine your process.
He talks about the way erroneous estimates balance out as "magic", but stresses that he has seen it work over and over and over.
The use of the Fibonacci series of points estimation is an acceptance that the bigger a story is, the less accurate our estimate is (see my earlier comment about Epics).
But, if it doesn't work for you, particularly if you keep all your jobs small, then don't use it. It's a guideline, not a rule.
T-shirt sizing (S M L XL XXL) is also popular and that is essentially no different from (1 2 3 4 5).