In our last post on Resource Management we showed you the Rule of 60s and how it is beneficial when planning resource allocation. That tool is primarily used for Planning and Managing your Portfolio rather than building project specific schedules. In our post today, I'll review the differences between using Effort vs Duration when building your Project Schedule.
Effort is the amount of time which will be spent completing a task or activity. Effort is often referred to as Work and in many Project Management Software tools Work is used rather than Effort. Effort is usually measured in hours.
Duration is how long it takes to complete the work. Effort and Duration aren't always, in fact rarely are, in a 1 to 1 relationship. Duration is usually measured in days.
For example, a task may required 8 hours of Effort to complete. The resource assigned that task will be working 4 hours for 2 days. The total Effort in this example is 8 hours and the Duration is 2 days. Got it? Pretty simple, right? Well maybe not so simple.
When working to build your schedules we always recommend starting with a WBS. The Work Breakdown Structure allows you and your team to identify the tasks to be worked on your project. The tasks are usually grouped to keep related tasks together. This is where the "Art of Project Management" comes into play.
The details of how to build your WBS is largely dependent on your organization and the size projects you deliver. A general rule of thumb is to not create any tasks in your WBS less than 8 hours and no task which is greater than 40 hours. The 8-40 Rule works well for most small to large projects. You may encounter Enterprise Projects that have extremely large tasks that go well beyond 40 hours. In that case, the 8-40 rule might be replaced by the 8-80 rule.
The 8-40 Rule used when building your WBS is based upon the Effort to complete each task. You then need to consider the resource(s) needed to complete the task, as well as the available Allocation of those resources to work on the task.
Let's create an example. We have a Project to paint a room in a school. We have 3 tasks in our WBS. Task 1 is Buy Supplies which has 8 hours effort. Task 2 is Prep the Room which has 24 hours effort. Task 3 is Paint the Room which has 60 hours effort. We have 3 Resources assigned to the project. 2 Resources are allocated at 6 hours per day and the other resource is allocated at 4 hours per day.
What is the Effort and Duration on the Project? The simple example above suddenly becomes a bit complicated. We have encountered many organizations which take the quick path and provide an estimate strictly using duration based on prior experiences. The resources huddle and tell the PM, "It's a small job it will take us 2 days." Maybe on a small job like that, that would work. But what if painting this one room was part of a larger project to paint the entire school?
Our recommendation is to take the time upfront and utilize your WBS, Resource Allocations, and other scheduling factors such as holidays, time-off, risks and issues to plan and build your schedule.
In our above example, Task 1 is assigned to Resource 3 and the 8 hours of Effort at 4 hours per day resulting in a Duration of 2 days. While Task 1 is Active, the other 2 resources are working on Task 2. Task 2 has 24 hours of Effort split between 2 resources who are available 6 hours per day. This results in a Duration also of 2 days. Both Task 1 and Task 2 are completed on day 2 so all 3 resources are available to work on Task 3 together. The Effort for Task 3 is 60 hours. The Duration is 3.75 days. Collectively, the 3 resources work 16 hours per day and finish the task on the 4th day. The total Effort on the project is 92 hours and the total Duration is 5.75 days, which greatly exceed the "it's a small job, 2 days duration" estimate.
Our guidance is to always let Duration be calculated. Use scheduling criteria such as Effort, Allocation, Task Relationship and other factors. Take the time to build your WBS and estimate the Effort or Work to complete each task. Your resulting schedule will prove to be more accurate than if you only estimate Duration without considering all the factors.
So how does that tie into Resource Management you ask? When you build your schedules calculating duration as we did above you get a more accurate understanding of the time resources will be working on tasks and projects. This more refined understanding of your Resources allows you to have greater confidence when planning within your Portfolio. If you are always behind schedule or short resources there is a good chance you are estimating Duration rather than calculating Duration.