What is Story Point Estimation?

Hi All,

Any body knows Story point Estimation? please explain with real time example. Thanks in Advance!

Replies to This Discussion

Permalink Reply by Bhumika on July 6, 2010 at 3:39pm

Story point is a sub part of Agile methodology. Here I am explaining how agile works.
For agile, the team (including customers, product manager, project manager, developers and testers) works in terms of sprint. Sprint is nothing but a full SDLC, for limited time period (in general for 3-4 weeks)
Agile methodology is useful while no requirements or rapid changes in requirements for the project.
For one sprint, the scrum master (generally the product manager) decides the tasks to be achieved.
For each task, separate story being created.
For each story, story points created (just to break the story in smaller parts) and then whole team estimates for particular story point and then the story point being freeze.
For Agile, each and every team member is involved in estimating (in terms of time to achieve the task) particular task / story point.

Hope it helps.

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Permalink Reply by Ashok Kumar M on July 6, 2010 at 10:12pm

Developers are, in general, more aware of the potential complexities that they can run into in the process of implementing a story. Despite this cognizance, it is often hard to predict exactly what these complexities might be. Obviously, if a developer knew the exact nature of the issues that he will run into, he can account for those and predict exactly how much time the work might take. Since this knowledge can never be complete, no developer can determine the exact amount of time needed.

Further, depending on the specific process being used in a given team, it is possible that the developer(s) who estimated a given story is not the one who ends up actually doing the implementation. Different developers have different skill levels and differing amounts of domain-knowledge. This also contributes to the variance in the actual time taken for implementation.

Finally, there are things that developers have no control over – the so called external factors – source-control going down or behaving erratically, having to attend meetings, or having to help another team or another developer on something, and so forth. Someone with critical knowledge could be out on vacation or a key developer could fall sick.

Lets represent actual time taken by a developer to complete a story with the following formula ->
A = function(C, U, E, S, K)
where
A = actual time
C = an idea of complexity (how difficult something is, and how many tasks there may be),
U = unpleasant technical surprises,
E = external factors,
S = implementing developer skill level,
K = available domain knowledge

Clearly, the only thing that can be “estimated” here is C – an idea of complexity (also based on the “understanding” of the team – whatever that is, and however it can be quantified). Let’s say that we measure this with complexity points (or story points). If we assume that everything else will get averaged out over the duration of the project (which it usually does), then it all comes together quite nicely. This is why story point estimation works.

On the other hand, trying to estimate using hours is like trying to guess the effect of the other four (and possibly more) factors. Trying to estimate in hours is like trying to estimate both the effort needed due to complexity AND the velocity of the people working on the story.

Finally, if I hear someone say that they have a capacity of 400 real hours, that they’re signing up for 600 hours of work and end up completing 500, then in my mind, the 500 hours of work that got done (which can’t be squeezed into 400 real hours) might as well be 500 story points. In fact, you can up the numbers by a factor of 10 so that the team really had 400 real hours (time doesn’t change), they signed up for 6000 points and got 5000 done, it will not change a thing. Story points are story points. The team can call it “ideal hours” or “estimate hours” or whatever they like. As long as they’re not real hours, they’re just like a rose with another name…