Tổng hợp Estimating: Analogous Estimating vs. Parametric Estimating vs. Three-point estimating vs. Bottom-Up Estimating

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.