Theory of Constraints Handbook - James Cox Iii [26]
Cause: Project managers are measured by their ability to meet their three objectives—complete projects on time, on budget, and to full specifications—whereas resource managers have the objective of utilizing their resources efficiently and are measured by their ability to keep resources fully utilized. These are conflicting objectives and have conflicting measures.
These are addressed by Guideline III.
Determining an Activity Time Estimate
In theory, we assume that the activity time is the mean time of the beta distribution (Miller, 1962). In reality, what time does the resource manager normally give? Is it the mean time? Seldom. Usually if a resource or resource manager is asked to provide a time estimate for a task, he or she pads the time a little (or a lot). If he or she ever misses that activity time and is chewed out by the project manager, then that time becomes more inflated to ensure successful activity completion. Think about it. If you provided a 50 percent task completion time estimate to your boss and were above the mean time 50 percent of the time, then your boss would probably think you were a poor worker. What probability of completion time do you give your boss? A completion time related to 50 percent or a time related to 95 percent? What if you finished the work early? Would you tell the project manager? You would probably not as his or her expectation would be that you should be able to complete future tasks in that amount of time. Yet, you gave the project manager a 95 percent probability of completion time to cover yourself. You would assume that if the project manager knew you finished early he would assume you provided inflated activity times and then would begin to question the time and costs you provided for other activities. Remember, we typically think the cost of a resource is based on the amount of time used by the resource to complete the job. If you consistently finished earlier than your time estimate, then the project manager would think you overpriced your resource. There is a strong tendency to both expand the time estimates of activities and, if the activity is finished early, not report the early finish.
Additionally, the project manager has a tendency to pad the project duration to ensure completion. Do you think the project manager is going to provide the boss a project completion time estimate that he or she is only 50 percent sure of completing? He or she probably gives a 95 percent probability of completion as well. You only have to be late one time on a major project to learn to pad your project times. What does the overall manager then do with your project time estimate? Cut the project time and cost and expect the same specifications. Why? The project manager started as a resource, then worked as a resource manager, then worked as a project manager, and is now a general manager and has practiced and knows the rules of the game.
Frequently, resources must be used to work on more than one activity at a time. Why? Two conditions come to mind. The first condition is the practice of multitasking discussed previously. The second condition exists where the resource runs into an unanticipated delay (interestingly the delay could be caused by a missing activity or a missing technological arrow on the network; hence, the need to use a beta distribution with pessimistic times) or must set aside the activity until later. This condition is discussed in the next section on identifying obstacles to completing an activity.
Cause: The rules and measures for determining activity time are ambiguous. For example, according to the assumptions of PERT theory, the resource (or resource manager) must provide a.5 probability time for activity times to build an accurate project network, yet the project manager expects a 1.00 probability of completion of the activity and project. If the resource finishes early or the project finishes early, then the expectation is for all of