Three-Point Estimation
Three-point estimation is the engine driving PERT. Instead of relying on a single, often flawed, guess for a task's duration, this technique forces you to define a range based on three specific perspectives:
Optimistic Estimate (O): The absolute best-case scenario. Think: "If everything goes perfectly – no interruptions, clear requirements, instant dependencies, no unexpected technical hurdles – what's the fastest this task could realistically be completed?" This defines the lower bound.
Pessimistic Estimate (P): The worst plausible scenario (excluding total catastrophe). Think: "If reasonable things go wrong – requirements are fuzzy, dependencies delayed, unexpected complexity arises, significant debugging needed – what's the longest this might realistically take?" This defines the upper bound.
Most Likely Estimate (M): Your most realistic assessment under normal conditions. Think: "Given typical minor issues, standard interruptions, and our experience, what's the most probable duration?" This is your anchor point.
Determining these three values collaboratively with the engineers doing the work is crucial. It leverages their specific knowledge and surfaces assumptions. The difference between P and O (the range) immediately quantifies the perceived uncertainty or risk associated with the task. It's a structured way to capture and analyze the variability inherent in development work.