Last month we started to have a look at more detailed facilities that Project provides to help us to examine and fine tune our projects. This month we’ll begin looking into the assignment of multiple resources.

Effort Driven

In Microsoft Project: Lesson 5—Working With Resources I commented that resource assignment can be very complicated. My advice is, if at all possible, keep to one resource per task and it is difficult to go wrong or fail to understand what’s going on. Remember, and I repeat: Effort-driven scheduling only takes effect when resources are added to or removed from a task. So, after the first assignment of a resource, effort driven scheduling has no effect unless you subsequently add or remove resources from the task.

So what happens if we assign more than one resource to a task? Project is an effort driven program. This is defined as a scheduling method that bases a task's duration on the amount of work the task requires and the number of resource units assigned to it: i.e., calculation is based on the formula:

Resource Units X Duration = Work

The values in the formula are set up for each task when a resource is first assigned; subsequent changes will be governed by the formula. There are several places in Project where you assign resources, but with multiple resources on one task you need a view that shows all the relevant parameters.

To illustrate this best, I always recommend using the split screen technique as in the following example. Let's have a project to make a garden with an initial plan that includes a pool of Gardeners. In a new project starting on 1 Mar 04, create a 10 day task: Make Terraces, then select it and then Window/Split.

You will see in the lower pane all the details we need to get the assignments right, i.e. the task Name and its Duration. There is the Effort driven selection (default is checked ON) and the Task type (default is Fixed Units) of which more later. On the left you can also see fields for the Resource Name, the Units assigned and the Work.

Click in the Resource Names cell and enter "Gardeners" and click OK (activating the OK button turns it and the adjacent button into Previous and Next to allow progression through the tasks.) You will see that Project assumes you want one full time gardener (100%) and for the Duration of 10 days it will consume 80 hours of Work (based on the default 8 hour day or 40 hour week).

Now, let's say it's going to take too long at 10 days, and to speed it up we assign another Gardener from our pool. So, change the Units value to 200% and click OK. Note that against the Gantt bar, the number of resources assigned is placed after the resource name if the Units are other than 100%. As this task is Effort Driven, the effort (Work) remains the same at 80 hours and thus Project reduces the Duration to 5 days - mission accomplished.

Play around with assigning more Gardeners and see the Duration reduce each time, and try less than 100%, say 50% meaning a Gardener only works half time per day (i.e. 4 hours per day, and thus to achieve 80 hours work, the Duration goes out to 20 days.) OK, changing the number of Units using the same resources from a pool is quite straight forward and works as one might expect with effort driven tasks. Restore the Units to 100% and the Duration should still read 10 days.

Different Resources

Fred from next door is a keen gardener and offers to help out. Click in the next Resource Name cell under the Gardeners and type in Fred and click OK. 

As you would expect the Duration again halves as they now both share the work: 40 hours each.

Suppose the task was still taking too long and you decide to add another Gardener. Click on the Gardeners’ Units and increase to 200% and OK.

You will see no change to the amount of work and the Duration doesn't change as you would have hoped. What has happened to the effort driven formula now? Well, you’ve presented Project with problem it cannot answer without guidance from you. It still upholds the 80 hours of work, but each Gardener is now only doing 20 hours whilst poor Fred slaves on for his original 40 hours. Thus, Fred becomes the driving resource as he still needs 5 days to finish. Try adding more and more Gardeners – the Duration remains the same based on Fred’s assignment. Equally, if you put in one gardener working half time (50%), the Duration goes back to 10 days, as that resource becomes the driving resource. (Remember always to click the OK button whenever you’re happy with the changes in order to get Project to calculate the new data. When you do, the buttons change to Previous and Next to allow you to progress through the tasks.)

You can see that blindly adding resources to a multi-resourced task my not achieve the reduction in Duration you want. You have to engage brain and be selective in your choice of resource assignment.

Now let’s try a different assignment. Remove Fred and assign 200% to Gardeners and ensure the Duration is 5 days with 80 hours Work. Now reassign Fred.

The Work is assigned equally between the 3 resources at 26.67% (Project rounds to 2 decimal places, though the real value is used in calculations) each, reducing the Duration to 3.33 days. Try experimenting with these assignments and try adding Mary and Joe, and also a material resource like Bricks, until you run out of explanation of why Project calculates as it does. Isn’t it easy to get into a mess!

In real life I have two prime tips:

·        Always use the split screen technique when you have more than one resource to assign so that you can see all the elements and the resulting calculations that Project makes.

·        If you run into problems, delete all the assignments from the task, reset the Duration and reassign them all to read what you want before you click the OK button: this in effect becomes the first assignment to that task and thus the effort driven formula will not come into effect until you click OK.

Next Month

I hope you will experiment with assigning resources in this way until you understand what is happening or, at least, be able to recover from any misplaced assignments. Next month we’ll have a look getting Project to do what you want with the assignments by seeing the effect of removing the effort driven setting and changing the Task Type.