Sensitivity analysis for resource scheduling

How sensitive are your project resources? I’m not asking if your team members shed a tear at their best friend’s wedding, I’m asking if you know which resources have the greatest effect on your project schedule.

The conventional approaches to resource limited scheduling are called resource levelling and resource smoothing. The first has the objective of keeping resource usage below your stipulated limits regardless of the effect this has on the time schedule. The second maintains the finish date calculated by a critical path calculation and smooths out the use of resources as much as possible.

The shortcoming of these two methods, as usually implemented in project scheduling software, is that they only give two possible solutions to the issue of juggling time and resource. There is actually a wide range of potential compromises between finishing the project by a specific date and performing it with specific levels of resource. Iterations of project completion date, resource availability and resources can provide a much more accurate picture of what are the key resources and how their availability affects the completion date. This is sensitivity analysis applied to resource scheduling. There are three types of iterations that can be performed:

1. If you have five resources, resource level just the first and note the project duration; then schedule the first and second and note the project duration. Continue adding resources and noting the duration until you are scheduling all five. You will probably notice that one particular resource creates the greatest delay. This is the resource to which the project schedule is most sensitive and is the one you need to focus on.
2. Having identified your most sensitive resource, you can note the effect of gradually increasing the amount of that resource. Once again, there is a good chance that one increment of additional resource produces a greater improvement in project duration than the others.
3. Another approach is to use resource smoothing and an imposed finish date to see how sensitive your resource overloads are to gradual extensions in project duration.  Set an imposed finish date on the final activity in your network and perform a resource smoothing calculation. Note the resource overload and then move the finish date out by a week and do it again. Once again, the chances are that one particular week’s delay will be the one that greatly reduces the resource overload. That is your balance between paying for additional resources and extending the project duration.

Of course, none of this deals with the most common situation, i.e. the one where you have a fixed end date and fixed limits on resources. Good luck with that one!