Critical Path Test

“A project without a critical path is like a ship without a rudder.”

- D. Meyer

In this check, DCMA runs a specific test to see whether or not they agree with the set of activities that are deemed critical. To do this, they use the constraint method.

What is the constraint method?

The constraint method is an alternative way to designate which activities and milestones are critical in a schedule network. The method works like this:

  1. Filter out all completed and summary tasks.

  2. Remove all hard constraints. Additionally, in Microsoft Project, remove all deadlines, because they can act like hard constraints.

  3. Identify the “final” task, the one that represents the project’s completion.

  4. Add a “finish no later than” constraint to that task, with a constraint date six months earlier than its baseline finish.

  5. Sort the total float column in ascending order. A set of tasks will be tied for the smallest total float, which should be a large negative number. Using a custom column (e.g., Text12 in MS Project), mark those tasks as “constraint method critical.”

  6. Remove the constraint that you added earlier from the final task.

  7. Compare what your scheduling tool deems critical (e.g., the critical column) with your custom field – what the constraint method marked as critical.

How does the constraint method highlight potential issues?

By removing the hard constraints in the second step, you are stripping the schedule down to its purest form; boxes and arrows that make up the schedule network. Step 4 (adding the “finish no later than” constraint) is the key. In this step, you’re finding the true longest path in the network. The group of tasks that shares the least (most negative) total float is on the longest path.

There may be differences between “constraint method critical” and what the scheduling program calls critical. Your next step is to examine and understand those differences. Technically, DCMA looks at tasks that are “constraint method critical” that the scheduling program is not marking as critical. Why is this? Because those are the tasks that DCMA believes are genuinely critical.

Next steps

If this check fails, the constraints in your schedule will typically be the culprits. You should be prepared to justify the inclusion of those constraints in the IMS. If there are no constraints in the schedule and this test still fails, it’s a good practice to run the other checks first and address any issues found. Several of the issues found by the other checks could be causing this check to fail.

14 Point Analyzer (via DCMA 14 point report)