Scope and the Triple Constraints of Quality, Schedule, and Budget

In today's post, I want to expand a bit on the relationship between the scope of a project, and the three fundamental constraints that get placed on that scope: schedule, budget, and quality.

We've all heard the old management joke: good, fast and cheap; you can maintain any two. But what does this actually mean? And how does it relate to the scope of deliverables of a project? I've been pondering this a bit lately, and being the engineer that I am, I had to draw some pictures to articulate my thoughts.

Imagine that the Scope of your project is represented by a triangle. Further, let's equate the extent of the delivered scope to the physical area of the triangle; the bigger the triangle, the larger or more extensive the delivered scope.

Then, to pin down this triangle's area, we're going to place at each of the triangle's corners so-called "constraints" that lock down the vertices and therefore fix the area, or delivered scope.  For example, at the top of the triangle is the quality constraint of the delivered scope. The position of this vertice defines the quality requirements of the scope.

Similarly, at the lower left of the triangle is the required time constraint in which you have to deliver the scope. And at the lower right is the budget constraint which you have maintain while delivering the scope. These three vertices together are referred to as the standard management "triple constraints" of a project, and essentially define the extent to which the scope can increase or decrease. In a sense, these area the boundaries in which you, the project manager, have to work to deliver the scope to the customer.

If we try to increase the quality of the delivered scope, for example, we represent this by pushing down on the top corner of the triangle-- and, because we want to maintain the delivered scope (i.e., the physical area of the triangle), one or both of the remaining vertices has to shift outward. Said another way, it's going to cost more money and/or take more time to deliver a higher quality product than was originally scoped.

In a similar manner, if we want to speed up delivery of the project's scope, we have to either add more money or resources to the project, or we have decrease the acceptance criteria (quality) of the delivered product. Or both. And the same holds true for cost; if our budget gets reduced, one or both of the other two scope constraints has to give somehow:

And finally, to extend this area-of-the-triangle analogy further, if we want to expand the scope of a project (i.e., increase the area), one or more of its corner constraints has to move outward; i.e., you will likely need either more money, more time, and/or have to reduce the quality requirements of the project:

Note that most projects have a priority that can be assigned to the triple constraints, with one or two having higher importance than the third. For example, if you were in charge of building a nuclear power plant, the constraint of quality would probably be much more important than that of schedule (i.e., it's more important that the nuclear reactor is of high quality than it gets built on time). Similarly, if you were put in charge of organizing and hosting a major event with the associated construction of major infrastructure, such as the Olympics, the constraint of schedule  (i.e., opening on time) is probably much more important to maintain than cost, and perhaps even quality.

Every project is different, but they all have similar reactions when putting pressure on their individual scopes. Your job as a project manager is to define these four things (scope + the triple constraints) at the beginning of the project, and then do your best to hold them all fixed in position throughout the life of the project. And when pressure is applied to that triangle, keep in mind which of the vertices are more important than the others.

© Copyright 2015 Mark H.Warner. All rights reserved.