Chapter 5: Estimating Project Times and Costs 4KF3

Transcription

1 Lecture Notes Importance of Estimates Support good decisions Schedule work o Make sure your team members can take on added work of project Determine length of project and costs o Projects can be cancelled because of lack of funds Determine worth of project Develop cash flow needs Determine progress of project Develop time-based budgets and establish project baseline Factors Influencing Quality of Estimates Planning horizon o The farther away the deadline, the more uncertainty Project duration People o People are hard to predict o The number of people o The skills people have Project structure and organization Padding estimates Organizational culture Other factors Estimating Guidelines for Times, Costs, and Resources Responsibility Use several people to estimate Normal conditions Time units Independence o Plan your projects as if all of the task are separate and independent regardless of if one might get backed up Contingencies Adding risk assessment to avoid surprises o Most likely scenario vs. least likely scenario Page 1 of 10

2 Top-Down vs. Bottom-Up Top-Down Approaches Consensus Methods Ratio Methods Apportion Methods Function Point Methods for Software and System Projects Learning Curves See Appendix 5.1 Bottom-Up Approaches Template approaches Parametric procedures applied to specific tasks Range estimating Hybrid Approach Phase Estimating Types of Costs Direct Costs Direct Project Overhead Costs General and Administrative Overhead Costs Refining Estimates Interaction costs hidden in estimates Normal conditions do not apply Things go wrong on projects Changes in project scope and plans Learning Curves Each time the output quantity doubles, the unit labour hours are reduced at a constant rate Studies have shown that human performance usually improves when a task is repeated Page 2 of 10

3 In general, performance improves by a fixed percentage each time production doubles More specifically, each time the output doubles, the worker hours per unit decrease to a fixed percentage of their previous value That percentage is called the learning rate The project manager should take the learning rate into account for any task where labour is significant Reading Notes Estimating: the process of forecasting or approximating the time and cost of completing project deliverables o Top-down (senior management) or bottom-up (workers) Project estimating becomes a trade-off, balancing the benefits of better accuracy against the costs for securing increased accuracy Factors Influencing the Quality of Estimates Past experience is a good starting point for developing time and cost constraints A typical statement in the field is to have a 95% probability of meeting time and cost estimates a) Planning Horizon Estimates of current events are close to 100% accurate but are reduced for more distant events Page 3 of 10

4 b) Project Duration Long-duration projects increase the uncertainty in estimates c) People Skills matching, turnover, employee productivity d) Project Structure and Organization Efficiency e) Padding Estimates Increase probability of meeting deadline f) Organization Culture How companies treat estimating g) Other Factors Downtime, national holidays, legal limits, etc. Estimating Guidelines for Times, Costs, and Resources a) Responsibility Estimates should be made by those most familiar with the task o They will have a better idea of what it takes o They will buy in to the project b) Use Several People to Estimate c) Normal Conditions Estimates should be based on normal conditions, efficient methods, and a normal level of resources d) Time Units All task time estimates need consistent time units e) Independence Estimates should treat each task as independent of other tasks that might be integrated by the WBS f) Contingencies Work package estimates should not include allowances for contingencies g) Adding risk assessment to the estimate helps to avoid surprises to stakeholders Top-Down vs. Bottom-Up Estimating Top-Down Estimates: usually are derived from someone who uses experience and/or information to determine the project duration and total cost Often made my managers who have very little understanding of the processes used to complete the project If possible and practical, it is best to push the estimating process down to the work package level for bottom-up estimates that establish low-cost, efficient methods. Page 4 of 10

5 Bottom-up estimates: at the work package level can serve as a check on cost elements in the WBS by rolling up the work packages and associated cost account to major deliverables. Resource requirements can also be checked. Methods for Estimating Project Times and Costs Top-Down Approaches for Estimating Project Times and Costs Consensus Methods o Using pooled experience of managers o Rough-cut and conceptual o Estimates are often off-the-mark because little detailed information is available but it shows whether a project warrants more investigation Ratio Methods o To understand need per units of a project Apportion Methods o Apportionment: used when projects closely follow past projects in features and costs (using history to estimate) Function Point Methods for Software and System Projects o Function points: weighted macro variables such as number of inputs, number of outputs, number of inquiries, number of data files, and number of interfaces Learning Curves o Improvement curves, experience curves, and industrial project curves o Each time the output quantity doubles, the unit labour hours are reduced a constant rate o Micro estimating methods are usually more accurate than macro Bottom-Up Approaches for Estimating Project Times and Costs Template Methods o Updating past project schedules to reflect new project o Development of standard templates can reduce estimate errors Parametric Procedures Applied in Specific Tasks Range Estimating o Range estimating: works best when work packages have significant uncertainty associated with the time of cost to complete A Hybrid: Phase Estimating Phase estimating: used when an unusual amount of uncertainty surrounds a project o Begins with a top-down estimate and then refines as the project moves forward o Uses a two-estimate system over the life of the project o Preferred when final product is not well understood o Even though the customer wants answers, they have the ability to make changes along the way Page 5 of 10

6 Level of Detail Delicate balance between WBS and management needs Types of Costs Direct Costs clearly chargeable to a specific work package o Labour o Materials o Equipment o Other Direct Project Overhead Costs can be tied to work packages or project deliverables General and administrative (G&A) overhead costs organizational costs not directly linked to a specific project Refining Estimates Why? o Interactions costs are hidden in estimates Work is not done independently in practice o Normal conditions do not apply Especially true when it comes to availability of resources o Things go wrong on projects Design flaws, extreme weather conditions, etc. o Changes in project scope and plans Unstable projects lead to cost overruns Creating a Database for Estimating Time and cost databases: professional estimating devices and estimators that respond to changes in estimates and develop as the project moves forward APPENDIX 5.1: LEARNING CURVES FOR ESTIMATING A worker can perform a task better/quicker the second time and each succeeding time she/he performs it (without any technological change). Each time the output quantity doubles, the unit labour hours are reduced at a constant rate. Page 6 of 10

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