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Chapter 7. Estimating the Work > Powerful Estimating Techniques and Methods
Powerful Estimating Techniques and Methods
There are several key estimating techniques you should know about. Table 7.1 lists these techniques and summarizes the key characteristics of each.
| Estimating Technique | Key Characteristics | Notes |
|---|---|---|
| Analogous (top-down) estimating | Used in early planning phases and project selection. Utilizes historical information (actual duration periods from previous projects) to form estimates. | Reliable if WBS from previous projects mirror the WBS needed for this project. |
| Bottom-up estimating | Used to develop detailed estimates.
Provides estimate for lowest level of the WBS (work package). Provides the most accuracy. | Best technique for identifying risk factors. Takes most time and money to develop. |
| Effort Distribution estimating | Uses project phase percentages to estimate.
Example would be Initiation Phase—10% Plan Phase—10% Elaboration Phase—20% Construction Phase—40% Deploy Phase—20% | Used in organizations that use common methodology and/or that do similar projects. Can be used if enough information is known for one of the major project phases. |
| Heuristic estimating | Based on experiences.
“Rule-of-thumb” estimating. Frequently used when no historical records are available. | Also known as Delphi technique and expert judgment. |
| Parametric estimating | Uses historical data and statistical relationships.
Developed by identifying the number of work units and the duration/effort per work unit. Examples include Lines of code for software development. Square footage for construction. Number of sites for network migration. | Also known as Quantitative-based estimating. Can be used with other techniques and methods. |
| Phased estimating | Estimates the project phase by phase.
Provides for a detailed, bottom-up estimate for the next phase and a higher level, top-down estimate for the other phases. Best technique to use on high-risk projects. | Incorporates “re-estimating” as part of the management approach. Best use of estimating resources. Excellent risk management tool. |
