How Long is a Football Game?

I asked this question to 2 colleagues and received the following responses:

 Colleague #1: 60 Minutes ( (4) 15 Minute Quarters)

 Colleague #2: 3 Hours (Games start Sundays at 1 and ends by 4)

So who is correct?  The answer: both.

Colleague #1 is correct because the actual time spent playing the game is 60 minutes (not counting potential overtime).

Colleague #2 is correct because it typically takes about 3 hours for the 2 teams to play 60 minutes of football.

So why am I talking about football?  Using this simple example, we can begin to understand why it is so hard to accurately estimate a projects.

If someone asks me how long it may take to do a particular task, I may answer 8 hours.  Let’s assume I work 8 hour days.  One of the next several scenarios can happen.

   Scenario #1: I finish the task in 1 working day.  The task really needed 8 hours of effort, and I had no interruptions so I was able to complete the task in 1 day.

   Scenario #2: I finish the task in 2 working days.  The task did take 8 hours of effort, but I had interruptions and was only able to work on the task 50% of the day (4 hours), so it took 2 days to complete.

In the above scenarios, was my 8 hours estimate wrong?  It depends, are we talking effort or duration?

In Scenario 1, effort was 8 hours and duration to complete that effort was 8 hours (1 day).

In Scenario 2, effort was 8 hours and duration to complete that effort was 16 hours (2 days).

Let’s add some additional scenarios for fun.

   Scenario #3: I finish the task in 1 working day.  The task really needed 4 hours of effort, and I had no interruptions so I was able to complete the task in 1/2  day.

   Scenario #4: I finish the task in 2 working day.  The task really needed 4 hours of effort, but I had interruptions and was only able to work on the task 25% of the day (2 hours), so it took 2 days to complete.

In Scenario 3, I was under on my effort (4 hours instead of 8) and under on my duration (4 hours instead of 8).

In Scenario 4, I was under on my effort (4 hours instead of 8) but over on my duration (2 days instead of 1).

And the list of potential scenarios goes on and on, and that is just for one task.  As you start to create a large list of tasks, it should be easy to see how the original plan can go way off.

Summary: Estimates are comprised of 2 elements, effort and duration.  Because we traditionally use the same unit for both elements (hours) it is often unclear on which we are estimating (effort or duration).  It is difficult to be accurate on both, since we face unknowns daily.