Our Scrum team has been having incomplete (not accepted) stories at the end of a sprint (usually 3 week sprint durations) that carry over into the next sprint. This has happened in every sprint except one in the team's 30 sprints.
We have tried to reduce the number of new story points that we accept in the next sprint relevant to the amount of carry-over. We also consider whether the remaining work on the carry-over stories is development and QA/testing or just QA/testing to try to avoid creating a bottle-neck in an area, since we are not cross-functional.
The reasons for the carry-over can be things like receiving incorrect test data that has to go through multiple cycles and lengthy processes in other systems, or the instability of the QA/test environment.
We are thinking of having a "clean up" sprint, where we would only accept critical, "must have" stories in order to reduce the committed story points and allow time to catch up on and close out any carry-over stories. This would allow us to start the first sprint in our next release with a "clean plate."
Have other teams done this and is it effective?
Should the duration of the "clean up" sprint remain consistent with previous sprints or be shorter (i.e. two weeks instead of our standard three)?
Best Answer
It looks like you aren't accounting for your velocity.
If you start with a sprint of 100 planning units, but only complete 90, your velocity is 90.
When you carry over 10 planning units, you should accept only 80 new planning units. That gives you a sprint of 90 planning units which matches your current velocity. If you find you are done before the scheduled end of the sprint, add more planning units to the following sprint.
If you carry over 10 planning units, and take on another 90 planning units, your sprint consists of 100 planning units. Based on the velocity of 90, you can expect to have 10 planning units of work left at the end of the spring.
Over time you will get a better idea of your velocity, and plan better. Expect variance in velocity between sprints. Planning units are estimates, not known quantities. With experience the estimates should get better and have lower variance.