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RE: [scrumdevelopment] BLOG on "How do Scrum and Critical Chain compare?

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  • Mike Cohn
    Simon-- If everyone on a team had the same skills (that is, no specialists) the resource buffers go away. At a high-level the synergy to me is that Scrum
    Message 1 of 2 , Nov 19, 2003
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      Simon--
      If everyone on a team had the same skills (that is, no specialists) the
      resource buffers go away.

      At a high-level the synergy to me is that Scrum buffers features, CCPM
      buffers schedule. However, in the real world I can't always run a project
      with the buffer entirely expressed in one dimension. By using Scrum to
      provide some buffering of features and CCPM for some buffering of time I can
      much more realistically go to a client and say "We should have 90% of that
      backlog done by June"

      --Mike

      -----Original Message-----
      From: Simon Coles [mailto:simon.coles@...]
      Sent: Wednesday, November 19, 2003 2:19 AM
      To: scrumdevelopment@yahoogroups.com
      Subject: RE: [scrumdevelopment] BLOG on "How do Scrum and Critical Chain
      compare?

      I agree that some of the buffer modelling techniques from CCPM can be
      borrowed effectively for initial planning, as Mike has done, however I don't
      believe that CCPM and SCRUM are truly synergistic as they are based on
      different very beliefs about managing change projects.

      SCRUM at it's heart is about self-organisation of teams and trust. The
      product owner sets the priority of the work to be done; the team tells the
      product owner what they can get done in the next 30 days.

      CCPM is fundamentally about centralised control. There are two types of
      buffer in CCPM: schedule buffers (such as Mike as has referred to) and
      resource buffers. Schedule buffers are derived from a belief that people
      will fritter away any slack time if you give them control of it (contingency
      belongs to the project as a whole). Resource buffers are derived from a
      belief that overall progress on a project is constrained by small numbers of
      specialist resources, and that success requires the PM to identify these
      resources and manage their time closely. This includes providing them with
      pre-notification of when they need to finish their current task in order to
      move onto the next.

      I'm sure that in reality CCPM is often implemented in a much more
      consensus-led way to the picture I've painted above, but at heart it's a
      fundamentally different beast to agile techniques.

      Simon

      -----Original Message-----
      From: Mike Cohn [mailto:mike@...]
      Sent: Monday, November 17, 2003 2:24 PM
      To: scrumdevelopment@yahoogroups.com
      Subject: RE: [scrumdevelopment] BLOG on "How do Scrum and Critical Chain
      compare? "



      In Clarke's message on Hal's blog he notes that he doesn't think anyone is
      combining Scrum together with Critical Chain.

      I've been combining the two since 1999 and agree that they are quite
      synergistic. I use Critical Chain techniques to provide an upfront forecast
      of how long a project will take. On our projects we collect two estimates
      for each item on the backlog (our backlog is generally in the form of XP
      stories). The first estimate is the "50% estimate" that represents how long
      something should take to code. If the programmer coded it 100 times this
      would be the time she'd take for the median. The second estimate is a 90%
      estimate--this is the "worst case" but not the *worst* in that no buses run
      anyone over, the source repository doesn't crash two seconds before backup
      and the building doesn't burn down. It's a realistic worst case. From these
      estimates we extrapolate a "project buffer". We then sum up the 50%
      estimates and add to them the project buffer to come up with the number of
      sprints we think something will take. It's been amazingly effective looking
      as far out as 9 months. (I haven't tried anything longer and don't really
      plan to.)

      So, we use CC to help give our Product Owner a more informed guess at the
      beginning and then once a sprint starts it's pretty much by-the-book Scrum.

      --Mike



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