It is vital to understand the difference between work and duration. A common (and poor) project management question is “How long will that take?”. Yet the answer may reflect the effort required (20 hours) or the duration (4 weeks) – clearly different responses meaning different things!
Here is a short video clip on the subject.
A recent blog looked at different tasks types in project management:
- Fixed Work
- Fixed Duration
- Fixed Units
It is important to recognise which task type you are dealing with when considering the work content and the duration.
Work Content of a Task
The work content of a task is the effort required to finish it completely. It will be the total of all the hours of effort by different resources to complete the task. Idle time, waiting, is not included in this total.
Duration of a Task
The duration of a task represents the total time for it to be completed. In one particular case, this will be the same as the work content, but only if one person is working full-time on the task, without any breaks.
The duration is often different from the work content because:
- There are more than one resources working on the task
- There is a gap between starting and completing the task (thinking time perhaps?)
- Resources may be diverted to different tasks or projects
- Resources may breakdown or take holidays
- There may be delays whilst we wait for a response from suppliers, contractors, or management.
Understanding the two different estimates of ‘Work’ and ‘Duration’ allow the project manager to understand more about the project, the tasks, and the resources.
Both ‘Work’ and ‘Duration’ are units of time, but considering the explanations above, are clearly different things. Therefore, it is good practice to use different units for each.
‘Work’ is often measured in hours, mainly because we can often identify costs by multiplying the ‘Work Content’ by an hourly pay-rate.
‘Duration’ can be measured in days, or weeks, depending on the length of the project. (Perhaps days for projects taking less than a year, and weeks for longer projects).
With this convention, the team will immediately recognise anything in ‘Hours’ denotes ‘Work’, and anything in ‘Days or Weeks’ denotes ‘Duration’.
Understanding the ‘Work’ and ‘Duration’ allows the project manager to probe deeper into estimates of tasks.
If somebody claims that there are 40 hours of work, and the duration is taking 1 week, then they are claiming that they are 100% efficient (unlikely) or that they are booking their inefficiencies to your project (likely).
Somebody telling you that 80 hours of work will be completed in 1 week, suggests that there are more than 1, probably more than 2 resources working on the task – suggesting questions about resource availability/skill levels etc.
If it is suggested that 10 hours of work will take 6 weeks duration, then the project manager needs to understand the reasons:
- Perhaps the task owner is on holiday
- Working on another project or task
- Waiting for machinery to become available
Once the real reasons are discovered, negotiations can take place to revise project/tasks priorities.
Work Profiles or Work Contours
Finally, work does not have to spread evenly through the duration. 20 hours of work across a 10 day duration does not mean that an even 2 hours of work will be done every day. (If it is that is a ‘Flat’ work contour).
Typically, there is more work performed at the start, the middle, or the end of the duration. These profiles or contours become important when balancing resource loading across many tasks and projects.
I have written a blog about applying work contours in Microsoft Project.
Work and Duration are different. Securing estimates for both can reveal a lot of information about tasks, and the resources executing them.