|
Estimations in Project Management
Biases in Estimation
You will find that you will have a difficult time remembering more than a few previous activities unless you spend some time to think about it and you will probably have a clearer memory of your most recent projects. It is also easier to recall your most successful or largest projects. Interestingly, in our example, the programmer does not perform actual time calculations; instead, based on his previous experience, he attempts to understand the likelihood that the task duration will be five days. During these few seconds, the programmer spent would have been able to recall a very limited number of his previous activities. Therefore, he is making his assumption based on very limited dataset. He calculates the likelihood of the task taking five days based on the projects he remembers and if he remembers only his successful activities, he will underestimate the duration.
To illustrate, below is the set of his previous activities relevant to his current task of developing a computer program to display a bar chart:
|
Date
|
Activity
|
Clearly
Remembers
|
Duration
|
|
Q1,
2001
|
Pie
chart
|
No
|
10
days
|
|
Q2,
2003
|
Interactive
bar chart
|
No
|
12
days
|
|
Q1,
2004
|
Multiple
line chart
|
No
|
7
days
|
|
Q2,
2004
|
Small
bar chart
|
Yes
|
3
days
|
|
Q4,
2005
|
Bar
chart
|
Yes
|
5
days
|
Since at the time of estimation the programmer only clearly remembers two out of the five activities, he deems it very probable that the activity will be completed in five days. In reality, it could take much longer.
Another interesting phenomenon in estimation is the
Rule of PI - regardless of how we do our estimations, we always underestimate, even if we are aware of the tendency to underestimate. Sound strange? Not if you think about it. Why are we repeatedly late and running out of time and money? We try to fit in too many activities into the project and hope against all hope that we will be successful. This wishful thinking is often the cause of the problem.
You can ask: Why PI? First, it emphasizes the fact that mistakes in estimations can be very significant. Second, this rule was invented by programmers who like to remind everybody that they know math.
Another interesting psychological phenomenon was mentioned by E. Goldratt in his Theory of Constraint. He calls it the
Student syndrome. It refers to the normal student style of preparations for an exam, which leads to the wasting any contingency buffers built into individual task duration estimates. A good example is how we saw that our programmer really concentrated on the job only when the deadline was looming.
|
solutions