Factors Influencing the quality of estimates
- Planning horizon
- Project duration
- people
- project structure and organization
- padding estimates
- organization culture
- other factors
Estimating guidelines for time,costs, resources
- Responsibility
- user several people to estimate
- normal conditions
- time units
- independence
- contingencies
- adding risk assessment to the estimate helps to avoid surprise to stakeholders
usually are derived from someone who uses experience and/or information to determine the project duration and total costs
Top-down estiamates
approach at the work package level can serve as a check on cost elements in the WBS by rolling up the work package and associated cost accounts to major deliverables
Bottom-up
note1:
at the strategic level top-down estimating methods are used to evaluate the project proposal
this method simply uses the pooled experience of senior and/or middle managers to estimate the total project duration and cost
consensus method
it is used when projects closely follow past projects in features and costs
Apportionment method
weighed macro variables
function points
it is the process of forecasting or approximating the time and cost of completing project deliverables
Estimating
Each time the output quantity doubles, the unit labor hours are reduced at a constant rate.
learning curve
works best when work packages
have significant uncertainty associated with the time or cost to complete
Range Estimating
used when an unusual amount of uncertainty surrounds a
project and it is impractical to estimate times and costs for the entire project
hybrid estimation
Why estimate?
- to support good decision
- to schedule work
- to determine duration of project and its cost
- to determine whether the project is worth doing
- cash flow needs
Costs that are clearly chargeable to a specific work package.
Direct cost
Costs incurred that are directly tied to an identifiable project deliverable or work package.
Project overhead costs
Organization costs indirectly linked to a specific package that are apportioned to the project
General and administrative overhead costs
Refining Estimates
- Interaction costs are hidden in estimates
- Normal conditions do not apply
- things go wrong on projects
- changes in project scope and plans
