One-point estimating | Three-point estimating | Bottom-Up Estimating | |||
Analogous Estimating (Top-Down) | Parametric Estimating | Heuristics | Triangular distribution (Simple Average) | Beta distribution / PERT (Weighted Average) | |
using historical data from a previous, similar activity or project | using a statistical relationship between historical data and other variables | A heuristic means a generally accepted rule, or best practice | Using three-point estimates helps define an approximate range => cover risk. Most likely (M): realistic expectations Optimistic (O): best-case Pessimistic (P): worst-case | Doing this type of estimating well requires an accurate WBS | |
– relies on the actual duration of previous, similar projects to estimate duration of the current project. – a gross value estimating approach, adjusted for known differences in project complexity. – less costly, less time-consuming, and less accurate. | This technique quantifies duration by multiplying the quantity of work to be performed by the number of labor hours per unit of work. Regression analysis (scatter diagram): This diagram tracks two variables to see if they are related; the diagram is then used to create a mathematical formula to use in future parametric estimating. | E = (O + M + P) / 3 Depending on the assumed distribution of values within the range of the three estimates, the expected duration (E) can be calculated | E = (O + 4M + P) / 6 This method gives stronger consideration to the most likely (M) estimate (x 4) SD = (P – O)/ 6 Activity standard deviation (SD) is the possible range for the estimate. SD = sigma (σ). | aggregating the estimates of the lower-level components of the WBS (activity or work package (if activities are not defined) | |
Uses this if the scenario indicates that you don’t have a lot of experience or historical info, Exam keyword: new project, no experience, not much reliable data, simple, straight. | Uses this if scenario indicates there are historical data or samples to work with Exam keyword: experts, similar to previous projects, need a more accurate estimate | ||||
the last five projects similar to this one each took eight months, so this one should as well. | If the assigned resource is capable of installing 25 meters of cable per hour, the duration required to install 1,000 meters is 40 hours | Design work is always 15 percent of the total project length or 80/20 rule | Terms like “simple” or “straight” refer to triangular distribution, “weighted” refers to beta distribution. Beta distribution leverages the benefits of risk management in reducing the uncertainty of estimates. | ||
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