Rock Paper Scissors vs. Fibonacci Numbers

I’ve picked up Kane Mar’s habit of playing rock, paper, scissors to estimate Product Backlog Items. This is a great way to get everyone’s estimate at the same time and provoke discussions between the outliers that wouldn’t happen otherwise. We go 1-5 for stories small enough to do in one Sprint, then 10, 50, 100, etc. for “epics” that need to be broken down into stories. The point is to communicate the numbers are rough guesses, not something to agonize over.

Another popular technique is to play “planning poker” using Fibonacci numbers. If a team is already using these I wouldn’t change it, but I don’t teach teams to start doing this. To do it right, everyone has to have cards with all the numbers on them, and show their cards at the same time. But estimation meetings can happen anywhere, any time you have the whole team together. The added bother of having to use the cards, plus the effort of explaining the Fibonacci sequence, plus the false impression there’s something magic about these numbers doesn’t seem worth it to me. My second choice (after rock, paper, scissors 1-5) would be powers of 2 I think. Most engineers have those memorized already, and it clearly communicates that the estimates are rough orders of magnitude.

UPDATE 12/17/06:
Mike Cohn writes that a lot of teams prefer the Fibonacci sequence.

If you do choose to use Fibonacci numbers I still recommend playing “planning poker” to get a cross section of opinions at the same time. I’ve attached a PDF with some cards of a modified Fibonacci sequence you can print on heavy stock and cut out.

UPDATE 2/2/07:
Another technique we’re finding pretty useful is T-shirt sizes with
corresponding powers of two. Registered users can download these here:
http://danube.com/system/files/T_Shirt_estimation_cards.pdf. Nonregistered users can
download these from the ScrumDevelopment Yahoo Group.

The Kinkos near my place was able to print these on card stock and
round the corners so they felt like regular playing cards. When we
get a round ‘tuit (besides the wooden one Jim Shore gave me) we’ll
get these printed onto real cards as Mike Cohn suggested and probably
give away some decks.

–mj

Michael James
Danube Technologies, Inc.
http://danube.com/blog/michaeljames/
http://scrumworkspro.com

fibonacci2.pdf13.48 KB

T_Shirt_estimation_cards.pdf1.2 MB

Michael James

Michael James is a software process mentor, team coach, and Scrum Trainer with a focus on the engineering practices (TDD, refactoring, continuous integration, pair programming) that allow Agile project management practices. He is also a software developer (a recovering "software architect" who still loves good design).

Posted in Agile
9 comments on “Rock Paper Scissors vs. Fibonacci Numbers
  1. Ralph says:

    I try to download the file http://danube.com/system/files/fibonacci2.pdf but access is denied. Can you please send the file via email?

  2. Michael James says:

    Sorry for the delay in responding — I was hunting rattlesnakes in Arizona on the back of a burro or donkey or something.

    It turns out our blogging software prevents downloads from people who aren’t registered on our website (which you’re welcome to do of course). If you prefer not to register here, I’ve also uploaded the file here:

    http://groups.yahoo.com/group/scrumdevelopment/files/fibonacci2.pdf

    The Danube thought trust got together just before Christmas and came up with some cards we think teams will like better using T-shirt sizes with corresponding powers of 2. If you’re interested in these please email me at michael@danube.com.

    Michael James
    Software Process Consultant
    http://www.danube.com

  3. Anonymous says:

    I want to download above sited link

  4. Michael James says:

    Note Danube is playing with the idea of releasing a physical card deck with T-Shirt sizes corresponding to powers of 2. We’ve found this communicates the idea better and avoids the problems of the Fibonacci sequence.

    Please contact me (michael@danube.com) if you’d like a free deck when we get around to this.

    –mj

    Michael James
    Software Process Consultant
    http://www.danube.com

  5. Josh says:

    I’m not any sort of engineer, but pushed hard for Fibonacci or powers of two when an old company was doing Scrum. It seems like the geometric scaling better represents the inherent variability of larger projects.

    The t-shirts seem interesting, and I applied to join the Yahoo group so I can see them, but any sort of explanation of of how they work/look would be appreciated.

    Thanks!

  6. Anonymous says:

    Interesting approach with
    http://groups.yahoo.com/group/scrumdevelopment/files/fibonacci2.pdf
    I will look even more into it.

  7. Michael James says:

    I’ve got a new batch of T-Shirt size cards with corresponding powers of two. Use the T-Shirt sizes for discussion, then record the powers of two for the purpose of prioritization and velocity tracking. For some reason people seem to grasp this more quickly than the other estimation methods.

    XS = 1
    S = 2
    M = 4
    L = 8
    XL = 16
    XXXXL = 128

    Use the XXXXL card for “epics” which need to be split into smaller stories before committing to a Sprint.

    Email me if you’d like me to send some of the cards I just made. Of course mine have the Danube logo on the back.

    –mj

    Michael James
    Software Process Consultant
    http://www.danube.com

  8. Michael James says:

    Alistair Cockburn writes that his favorite estimation sequence is “3, orange, pencil, cloud.” I love it!

    http://tech.groups.yahoo.com/group/extremeprogramming/message/140650

    –mj

    Michael James
    Software Process Mentor
    http://www.danube.com

  9. Vivek1311 says:

    Agile guys have really lost it – using Fibonacci numbers for an estimation techinique, or T-shirt sizes !!

    What’s going to be next ?

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