Weekend Puzzler: Computing Critical Path Drag on a Project to Save Lives

There has been a lot of discussion of critical path drag and drag cost recently, both in this blog and elsewhere. Most salient was Blake Sedore’s MIT paper about using critical path drag to optimize manufacturing throughput, but there was also this very nice out-of-the-blue comment on LinkedIn, and a number of email conversations. Maybe the importance of these concepts is finally trickling into general awareness.

So with the weekend here (a long one in the US!), I decided it was time to provide another “Weekend Puzzler” of practice in computing drag and drag cost. So I’ve drawn a network diagram below, with all the dependencies finish-to-start (FS), just to make sure it isn’t too complicated. And if there is any step you feel is too complicated or tedious (perhaps like the forward and backward passes), just jump over it to the next diagram, which will have the answers.

To emphasize the importance of these computations, I’ve chosen a project that is intended to save lives: an immunization program, hospital construction, or medical device development, perhaps. But the calculations would be the same if the only benefits were monetary.

After the fourth diagram, there are some additional questions, with the “poll” function making it a multiple choice quiz. I’ll provide the answers and explain them on Tuesday.

And by the way, next week should be interesting in any case. I am hoping to launch a discussion forum, where readers can raise topics they want to discuss, or make general comments. Additionally, I believe the June issue of PMI’s PM Network magazine will become available on-line, and I have reason to believe there may be a very interesting article in this issue.

Have a great weekend, and the Puzzler is directly below.

Fraternally in project management,

Steve the Bajan

Weekend Puzzler

A.  Compute the forward and backward passes for early and late dates, identify the critical path and compute total float.

Fig 1 All FS network lives for blog

B.  These are the answers to A. Now compute the drags of the critical path activities.

Fig 2 All FS network lives for blog

C.  These are the answers to B. Now compute the drag cost in lives not saved for each of the critical path activities.

Fig 3 All FS network lives for blog

D.  These are the answers to C. Use them to answer the multiple choice questions in the “poll”.

Fig 4 All FS network lives for blog

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