Story Points Do Not Equal Development Hours
23 December 2015
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One of my regular challenges is how to estimate a user story by using the number of days or hours necessary to complete the work. Management directly maps the number of story points to the number of days. For example, one story point is equal to one ideal day, which is equal to six hours. There could be two reasons for this simplistic approach. First, it is similar to the Waterfall model for estimation, which most of management is used to. Second, this gives them a so-called quantitative way of communicating the budget and deadlines to management.
While the mapping idea may seem good on paper, it often leads to individuals working toward unrealistic deadlines and estimation clashes during planning. Although story points are estimated mostly by senior developers, a new member will most likely ask for more time to complete the same work.
It's important to note that story point estimation is high-level estimation and shouldn't be used to measure the time it takes to complete a user story. Only after user stories are committed for an iteration can you make hourly estimations for tasks. Task estimation is relative and depends on the individual's capacity and experience. This means that a story point can take four hours, eight hours, or 16 hours, depending on the individual's capacity. At the end of the iteration, we should be able to calculate the team velocity. For a newly formed team, the velocity measure in the initial few sprints can help with figuring out the time needed to complete a feature or a release.
Ideally, story points should be a measure of the amount of work involved instead of the number of hours. That is the reason that Scrum specialists use abstract values, such as t-shirt sizes, to represent story points. This approach to estimation helps us to avoid conflicts during the planning meetings, because the scope of work will remain the same, irrespective of the individuals.
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