According to the PMBOK® Guide, specifically within the Estimate Activity Durations process, the primary principle for achieving accuracy in scheduling is to involve the individuals who will actually perform the work or those with the greatest expertise in the specific functional area.

In the PMI framework, duration estimates should be provided by the person or group on the project team who is most familiar with the nature of the work in the specific activity.

Expert Judgment: This is a primary Tool and Technique for estimating. The individual with the most familiarity provides " expert judgment " based on historical experience, technical nuances, and potential pitfalls that a generalist might overlook.

Accuracy and Buy-in: When the person responsible for the task provides the estimate, it leads to a more realistic schedule. Furthermore, it creates a sense of commitment and accountability; a team member is more likely to meet a deadline they helped set than one imposed upon them.

Bottom-Up Estimating: This approach is part of the broader " Bottom-Up " philosophy where the granular details are defined by the technical experts and then rolled up into the total project duration.

A. Project sponsor: The sponsor provides the project ' s funding, high-level requirements, and authorization (Project Charter). They generally do not have the granular, technical knowledge required to estimate specific task durations.

B. Project manager: While the Project Manager facilitates the estimating process and " owns " the final project schedule, they are often a generalist. They should not provide the original estimates themselves unless they are also the primary subject matter expert for that specific task.

C. Person responsible for project scheduling: A scheduler or " Project Scheduler " is responsible for the mechanical act of building the schedule model using software. They take the duration data provided by the team and input it into the tool; they do not typically generate the original duration data themselves.

The Estimate Activity Durations process utilizes several techniques to refine the inputs provided by the person most familiar with the task, including:

Analogous Estimating: Using a similar previous project.

Parametric Estimating: Using a statistical relationship (e.g., hours per square foot).

Three-Point Estimating: Using Optimistic, Pessimistic, and Most Likely values to account for uncertainty.

Regardless of the technique used, the Subject Matter Expert (SME) remains the foundational source of the raw data.