Have you considered the cost of context switching

One of the great things with running a project with Microsoft Project is that it enables you to allocate resources to activities and you can assign the time they work on each activity.  A resource can then work on several projects at the same time, 50% on project A, 50% on project B.

With this ability it is easier to accommodate multiple projects that the business request.  Rather than having to say we can’t start on a project in six months when the current one finishes, we can run both projects at the same time, using the same resources.  We can do things in parallel rather than in series.

Only it doesn’t really work like that.

One of the great things with running a project with Microsoft project is that it enables you to allocate resources in a way that hinders productivity, effective planning and quality.

The problem is with context switching and the overhead that multi-tasking brings.  This article succinctly describes the problem.

No matter how efficient you think you are, multitasking comes with a high cost. Because we’re people, we don’t swap out the content of our brains as easily as a computer does, and we definitely don’t swap in the old state when we’re ready to return to the original task.

Gerald Weinberg, in Quality Software Management, Vol. 1, Systems Thinking (Dorset House, 1992), estimates the context-switching cost among three tasks to be 40 percent. That means that 40 percent of your available work time is spent on non-task activities. The rest of the time is split among the three projects. So, if you thought that in a 45-hour week, you could spend 15 hours on each of three tasks, don’t kid yourself. You’re really spending eight hours on project A; eight hours on project B; eight hours on project C; and 24 hours context-switching, figuring out where you were and what you have to do next. The time spent on each project works out to about half of what you expected.

So whilst it is easy to appear to please business sponsors by taking multiple projects on at the same time, and the model of working in parallel rather than in series being a politically favourable approach, in fact the costs of multi-tasking far outweigh the benefits.

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