## Project duration and Task Estimations

Hi,

how often did you hear questions like those two:

1. How much time do you need to fulfill this Task?
2. When do you expect Project to finish?

Those two questions are most common when we talk about time in Project. And yes, they are regular, and expected. Where is the problem then? The problem is that someone who ask those question will rely on your answers. And if you are going to be late, that person (we also call them: Management, Customers, Clients) will tell you: “But you told me that you will be finished until….”

Let’s face it! When you are in IT, you know that it is impossible to promise that something will be finished as you told. Why? Because when we are preparing answers on questions mentioned above we are doing estimations! Read again – E S T I M A T I O N S!

What is estimation, anyway? Estimation (or estimating) is the process of finding an estimate, or approximation , which is a value that is usable for some purpose even if input data may be incomplete, uncertain , or unstable. The value is nonetheless usable because it is derived from the best information available.

Based on definition above, you will find that estimation is always unstable, because you are estimating something what should be done, what is unique (no matter how many times you did a similar task before). Yes there are many estimation processes. PERT is one of them. In PERT you will estimate Optimistic, Pessimistic ans Most Likely time, and standard deviation. For example your Task has:

1. Optimistic time = 1 day
2. Pessimistic time = 9 days
3. Most Likely time = 2 days

PERT is (Optimistic Time + Pessimistic Time + 4 * Most likely Time)/6 = (1+9+4*2)/6 = 18/6 = 3 days! And Standard deviation is (Pessimistic time – Optimistic time)/6 = (9-1)/6 = 8/6 = 4/3 = 1,333 days. So, your final estimation is 3+/-1,333 days which mean that in best case your Task will have 1,67 and in worst case  it will have 4,333 days of duration.

BUT! How did you get your Optimistic, Pessimistic or Most Likely time? You think, and think, and talk to you colleagues (if you have them, and if they have enough knowledge), and then – make an unreliable estimation. Something the real time spent on your Task will be very close to your estimated time, sometimes it will e far away, and sometimes (HURAAAA) it will be exact the same as estimated time.