HKSM

A method for estimating cost or duration by combining optimistic, most likely, and pessimistic values into a simple or weighted average, used when activity estimates are uncertain.

Key Points

• Captures uncertainty with three inputs: optimistic (O), most likely (M), and pessimistic (P).
• Two common expected-value formulas: Triangular = (O + M + P) / 3; PERT (weighted) = (O + 4M + P) / 6.
• Can quantify variability: standard deviation often taken as (P - O) / 6 and used to form ranges.
• Applies to activity cost, duration, or effort and is typically based on expert judgment and historical data.

Example

A task to configure a server has O = 4 days, M = 6 days, P = 12 days. Triangular estimate = (4 + 6 + 12) / 3 = 7.33 days. PERT estimate = (4 + 4*6 + 12) / 6 = 6.67 days. Standard deviation = (12 - 4) / 6 = 1.33 days, so a rough range is about 6.67 +/- 1.33 days.

PMP Example Question

Which estimating technique combines optimistic, most likely, and pessimistic values to produce an expected duration and can also indicate variability?

1. Analogous estimating
2. Parametric estimating
3. Three-point estimating
4. Reserve analysis

Correct Answer: C — Three-point estimating

Explanation: Three-point estimating uses O, M, and P to compute an expected value (triangular or PERT) and can provide a standard deviation to express uncertainty.