Actual schedule becomes better known as the project unfolds.

Goal - Minimize magnitude of the uncertainty at project start.

Update estimates throughout project.

Without a schedule estimation method, expect the initial estimate to be off by as much as 400%

Estimation methods (in order of effectiveness) include:

#1 Bottom-Up

• Identify functional characteristics of the system.
• Estimate effort to create the functionality.
• Total the effort to arrive at the completion date.
• Uses formal methods such as Function Point Analysis and/or COnstructive COst MOdel (COCOMO).

#2 Analogy

• Project is similar to previous projects.
• Requires keeping project history data so that future projects can benefit from metrics.

#3 Top-Down

• Decomposition of tasks into subtasks.
• Estimate the time required for each subtask.
• Some tasks may be concurrent, or may be dependant on other tasks.
• Total the time to get the completion date.
• MS Project encourages this approach.

#4 Price-to-Win

• Low-ball bid to win contract.
• May result in unacceptable tradeoffs between cost, schedule, and quality.
• Generally results in long, uncompensated overtime hours.

#5 Dictated by Circumstances

• External forces may dictate the cost, schedule, or quality.
• Requires high degree of flexibility in the non-dictated factors.
• Must verify that the dictated circumstances are real and not imaginary.

#6 Guess

• Scratch head and pull out dates. “I think it will take, hmmmm, 2 weeks.”
• According to IBM studies, guesses are typically off target by 200% to 400%..
• Indicative of companies that use project planning tools, but do not have the methodologies or mindset

Program Evaluation and Review Technique (PERT).

• Weighted average approach improves quality of estimate.
• Can be used in conjunction with any approach except Dictated by Circumstances.
• Obtain three estimates for each task: the most optimistic, the most likely, and the most pessimistic.

Time = Optimistic + 4xMostLikely + Pessimistic
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