Managing the Triple Constraint

The PMBOK mentions the three main variables of a project several times. Each of these variables is related to the other two and directly affects the quality of the project. The three variables are called the triple constraints and must all be managed to successfully complete a project. Each of these three variables tends to compete with one the others. Too much attention on one generally means one or both of the others suffer. A major concern of the project manager is to ensure each of these variables is balanced with the other two at all times. The three variables of the triple constraint are

• Project scope How much work is to be done? Increasing the scope causes more work to be done, and vice versa.

• Time The schedule of the project. Modifying the schedule alters the start and end dates for tasks in the project and can alter the project's overall end date.

• Cost The cost required to accomplish the project's objectives. Modifying the cost of the project generally has an impact on the scope, time, or quality of the project.

Any change to one of the variables will have some effect on one, or both, of the remaining variables. Likewise, a change to any of the three variables has an impact on the overall quality of the project. The key to understanding the triple constraints is that they are all interrelated. For example, if you decrease the cost of your project, you will likely decrease the quality and perhaps even decrease the scope. With less money, less work gets done. Or, you might find that it takes more time to produce the same result with less money. Either way, a change to cost affects other variables.

Even though this concept is fairly straightforward, a project manager must stay on top of each one to ensure they are balanced. In addition to managing the triple constraints, the project manager is also responsible for explaining the need for balance to the stakeholders. All too often, stakeholders favor one constraint over another. You'll have to ensure that the stakeholders understand the need for balancing all three.

Figure 1.4 shows how the triple constraints are often depicted as a triangle, with quality in the center.

Figure 1.4. The triple constraints.

Understand how the triple constraints require balance to ensure a change does not negatively impact another variable.