March 6, 2007 – Deliverable-based Project Schedules: Part 6

All the tasks have been laid out, sorted into deliverables, aligned with predecessors and estimated for effort. If you are using an auto-scheduling tool like MS Project, the length of the project has been stretched out as if one person was doing everything at 100%. Now we want to set realistic expectations on the duration of each task.

Estimate Duration. “Why are we worried about the duration before we add the resources?” you might ask. Good question. The reason is productivity. It is easier to bake it in up front than to try and force it in later.

Mentally everyone knows that, unless you work overtime, an 8-hour task takes more than a day to complete. This is a factor of our productivity. Over the course of a year people are, at most, about 80% productive. This is based on the following calculation.
2080 hours in a year (52 weeks * 40 hours / week)
- 72 hours for holidays
- 80 hours vacation
- 48 hours sick time
- 24 hours training (non-project related)
- 52 hours status reporting (1 hour / week)
- 52 hours team meetings (1 hour / week)
- 88 hours interruption (1.5 hours / week)
1664 hours remaining (80%).

Obviously some people have more vacation, others don’t get sick, some have more training, etc. but in general this holds true. Without taking this into account at the task level you are setting yourself up to be late.

Some project managers do this by assigning all of their resources at 80% available. In MS Project there is a resource field named Max Units that they set to account for the productivity factor. Unless someone is assigned to my project only part time, I keep them at 100% available and set the duration of the individual tasks to account for the extra time. After all, they are still expected to work 100% of the time.

MS Project allows you use a custom field to automatically calculate the 80% rule. To do this use the Duration 1 field and create the formula [Work / 0.8]. This will calculate 8 hours as 1.25 days and 40 hours to be 6.25 days. If you place the Duration 1 column in the schedule beside Duration, you can easily copy and paste the estimated values into the Duration column.

You can also type it manually for each task using the 8 and 40-hour duration estimates as guidelines.

When we add multiple resources to a task, they are each assigned at 80% to it. They will still be assigned 40 hours of effort for the week, but the tasks will be spaced to account for interruptions, status reporting, overlapping tasks, etc.
The resulting durations are starting points. After you add resources and begin to use and refine your schedule you can make adjustments to them.

March 5, 2007 – Deliverable-based Project Schedules: Fixed Work Sidebar

Before we move on to discussing duration and adding resources there is a side step we need to take to discuss different task types. When you are developing your project schedule, most tasks should be set as Fixed Work. As effort is expended or added to the task this allows the tool to re-calculate the duration and show the new estimated completion date.

In MS Project there are 3 types of tasks: Fixed Duration, Fixed Units and Fixed Work. I’m sure other scheduling tools have similar terms. Units (U) refers to the percent a resource is assigned to the task (the productivity factor discussed above). Duration (D) is the number of days a task takes to complete. Work (W) is the amount of effort expended or to be expended on the task. The formula for calculating Duration is D = W / U (ex. 8 hours / 80% = 10 hours = 1.25 days). This equation and variables are used to determine when the task will complete.

“Fixing” one of these variables tells the tool not to allow it to change. If Duration is fixed and you add more Work, the Units will increase to balance the equation. In order to complete a 16-hour task in 1 day the resource will need to be assigned 200%. If Units are fixed at 100%, reducing the Duration of a 16-hour task from 2 days to 1 day will force the Work to 8 hours in order to maintain the equation. Neither one of these options helps you track progress.

Selecting Fixed Work is more realistic. If you have an 8-hour task scheduled for 1 day and you decide to extend it to 2 days you want the Work to remain at 8 hours, not increase to 16. The time you allowed for the completion of the task increased, not the effort to do it.

This is a big topic from project managers trying to figure out what MS Project is doing to them. They change a duration or end date and suddenly the estimated hours either explode or shrink to nothing. Very frustrating.

On the flip side, there are tasks that should be Fixed Duration. These tasks include support, status reporting and others that are based on the calendar rather than the effort. Although I have never used it, there is probably a good application for Fixed Units. If you have an example, add a comment to this blog and I’ll pass it on.

The task type becomes important as we move to estimating the duration.