This issue is best addressed by recognizing a distinction between “competing demands” and “constraints.” Because the traditional triple constraints are included among the five competing demands, some readers may get confused.
On page 6 of the PMBOK Guide (2000 Edition) we find the following statement: “The project team manages the work of the project, and the work typically involves competing demands for scope, time, cost, risk, and quality.” Ok, I can accept that.
On page 199 of the PMBOK Guide (2000 Edition) we find the following DEFINITION of a constraint: “Constraint: Applicable restriction that will affect the performance of the project. Any factor that affects when an activity can be scheduled.” Carefully note the word “can” in the last sentence.
It might be helpful to remember that the word triple means three (3), and then focus on the second portion of the definition offered in the PMBOK Guide. Constraints are those “restrictions” (objective criteria) that affect when an activity can be scheduled. Those “restrictions” would be SCOPE, TIME, & COST.
A comprehensive definition probably would read more like the following: “Scope, time, and cost have traditionally been referred to as the ‘triple constraints’ affecting project scheduling. Of course, experienced project managers recognize that project planning involves competing demands for scope, time, cost, risk, and quality.”
Note the intentional mapping of “triple constraints” to project scheduling and “competing demands” to project planning in the preceding paragraph.
For an example, imagine yourself looking at a specific task in an MS Project schedule. You will notice that you can change the name (SCOPE), you can change the start & end dates (TIME), and you can change the resources (COST). Where is the field in the task record to address the “risk” or “quality” demands? You will find that they are not there. Of course, you can supplement the task information (add a note) to address these demands.
An argument could be made that risk is included in COST and quality is included in SCOPE. However, it is much more difficult to argue that SCOPE, TIME, or COST are included in one of the others. Fortunately, the PMBOK Guide Third Edition includes some clarification that is consistent with my explanation above. See page 8 second or third paragraph.
Some reference books use “Time, Cost, Performance” as the triple constraints, and some of those books likely are in the room for reference (along with the PMBOK Guide) as PMP volunteers are creating questions. It is highly unlikely that Kim’s or Rita’s (or any other) PMP Exam Prep books are available in the room for reference as volunteers are creating questions. A final comment. When it comes to the PMP Exam, the PMBOK Guide rules. The PMP Exam reflects a consensus opinion of dozens of PMP Exam item-writing volunteers who are all PMPs from many different industries and countries.
David David J. Lanners, MBA (Harvard) CFPIM, CIRM, CMC, CQA, CQE, CQMgr, CVS, PMP
Lead Instructor & Executive Consultant LCS International, Inc., Dallas, Texas