第六章_Project schedule management_(第二部分)项目管理英文第六版
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• Develop Schedule is the process of analyzing activity sequences, durations, resource requirements, and schedule constraints to create a schedule model for project execution and monitoring and controlling.
– A 15% probability of exceeding 3 weeks, which indicates a high probability—85%—that the activity will take 3 weeks or less.
10
Causes of Variation
Causes of Variation in the Actual Activity Duration
• When estimating durations, this technique relies on the actual duration of previous, similar projects as the basis for estimating the duration of the current project.
• The detail durations are estimated. • These estimates are then aggregated into a total quantity for
each of the activity’s durations.
9
Duration estimates
• Depending on the assumed distribution of values within the range of the three estimates, the expected duration, tE, can be calculated.
– One commonly used formula is triangular distribution: tE = (tO + tM + tP) / 3.
6
Parametric estimating
• Parametric estimating is an estimating technique in which an algorithm is used to calculate cost or duration based on historical data and project parameters.
• Analogous estimating uses parameters from a previous, similar project, such as duration, budget, size, weight, and complexity, as the basis for estimating the same parameter or measure for a future project.
• The schedule model is used to determine the planned start and finish dates for project activities and milestones based on the best available information.
5
Analogous estimating
• Analogous estimating is a technique for estimating the duration or cost of an activity or a project using historical data from a similar activity or project.
– Optimistic (tO). The activity duration based on analysis of the bestcase scenario for the activity.
– Pessimistic (tP). The duration based on analysis of the worst-case scenario for the activity.
• Duration estimates are quantitative assessments of the likely number of time periods that are required to complete an activity, a phase, or a project.
• Parametric estimating uses a statistical relationship between historical data and other variables (e.g., square footage in construction) to calculate an estimate for activity parameters, such as cost, budget, and duration.
• The key benefit of this process is that it provides the amount of time each activity will take to complete.
2
Estimate Activity Durations
3
Estimate Activity Durations: Data Flow Diagram
• These estimates are used to approximate the number of work periods (activity duration) needed to complete the activity using the appropriate project and resource calendars.
• Other factors for consideration when estimating duration include:
– Law of diminishing returns. – Number of resources. – Advances in technology. – Motivation of staff.
4
ቤተ መጻሕፍቲ ባይዱ
Estimate Activity Durations
• The Estimate Activity Durations process requires an estimation of the amount of work effort required to complete the activity and the amount of available resources estimated to complete the activity.
• Duration estimates may include some indication of the range of possible results.
• For example:
– A range of 2 weeks ±2 days, which indicates that the activity will take at least 8 days and not more than 12 (assuming a 5-day work week); or
Software Project Management
Project schedule management
Estimate Activity Durations
• Estimate Activity Durations is the process of estimating the number of work periods needed to complete individual activities with estimated resources.
• Unexpected events. Random acts of nature, vendor delays, traffic jams, power failures, etc.
• Efficiency of work time. Every time a worker is interrupted it takes more time to get up to the level of productivity prior to the time of the interruption. These interruptions may have little or substantial impact on the worker's productivity
• Mistakes and Misunderstandings. In organizations that have a documented process, rework may have its toll on the actual activity duration.
11
Develop Schedule
• Varying skill levels. Our estimate of the activity duration is based on average skilled engineer. We may get a higher or lower skilled engineer assigned to the activity, causing the actual duration to vary from the planned duration.
7
The accuracy of single-point duration estimates
• The accuracy of single-point duration estimates may be improved by considering estimation uncertainty and risk.
8
Bottom-up estimating
• Bottom-up estimating is a method of estimating project duration or cost by aggregating the estimates of the lower level components of the WBS.
• Using three-point estimates helps define an approximate range for an activity’s duration:
– Most likely (tM). This estimate is based on the duration of the activity, given the resources likely to be assigned.
• When an activity’s duration cannot be estimated with a reasonable degree of confidence, the work within the activity is decomposed into more detail.
• The key benefit of this process is that it generates a schedule model with planned dates for completing project activities.
• Developing an acceptable project schedule is an iterative process.
– A 15% probability of exceeding 3 weeks, which indicates a high probability—85%—that the activity will take 3 weeks or less.
10
Causes of Variation
Causes of Variation in the Actual Activity Duration
• When estimating durations, this technique relies on the actual duration of previous, similar projects as the basis for estimating the duration of the current project.
• The detail durations are estimated. • These estimates are then aggregated into a total quantity for
each of the activity’s durations.
9
Duration estimates
• Depending on the assumed distribution of values within the range of the three estimates, the expected duration, tE, can be calculated.
– One commonly used formula is triangular distribution: tE = (tO + tM + tP) / 3.
6
Parametric estimating
• Parametric estimating is an estimating technique in which an algorithm is used to calculate cost or duration based on historical data and project parameters.
• Analogous estimating uses parameters from a previous, similar project, such as duration, budget, size, weight, and complexity, as the basis for estimating the same parameter or measure for a future project.
• The schedule model is used to determine the planned start and finish dates for project activities and milestones based on the best available information.
5
Analogous estimating
• Analogous estimating is a technique for estimating the duration or cost of an activity or a project using historical data from a similar activity or project.
– Optimistic (tO). The activity duration based on analysis of the bestcase scenario for the activity.
– Pessimistic (tP). The duration based on analysis of the worst-case scenario for the activity.
• Duration estimates are quantitative assessments of the likely number of time periods that are required to complete an activity, a phase, or a project.
• Parametric estimating uses a statistical relationship between historical data and other variables (e.g., square footage in construction) to calculate an estimate for activity parameters, such as cost, budget, and duration.
• The key benefit of this process is that it provides the amount of time each activity will take to complete.
2
Estimate Activity Durations
3
Estimate Activity Durations: Data Flow Diagram
• These estimates are used to approximate the number of work periods (activity duration) needed to complete the activity using the appropriate project and resource calendars.
• Other factors for consideration when estimating duration include:
– Law of diminishing returns. – Number of resources. – Advances in technology. – Motivation of staff.
4
ቤተ መጻሕፍቲ ባይዱ
Estimate Activity Durations
• The Estimate Activity Durations process requires an estimation of the amount of work effort required to complete the activity and the amount of available resources estimated to complete the activity.
• Duration estimates may include some indication of the range of possible results.
• For example:
– A range of 2 weeks ±2 days, which indicates that the activity will take at least 8 days and not more than 12 (assuming a 5-day work week); or
Software Project Management
Project schedule management
Estimate Activity Durations
• Estimate Activity Durations is the process of estimating the number of work periods needed to complete individual activities with estimated resources.
• Unexpected events. Random acts of nature, vendor delays, traffic jams, power failures, etc.
• Efficiency of work time. Every time a worker is interrupted it takes more time to get up to the level of productivity prior to the time of the interruption. These interruptions may have little or substantial impact on the worker's productivity
• Mistakes and Misunderstandings. In organizations that have a documented process, rework may have its toll on the actual activity duration.
11
Develop Schedule
• Varying skill levels. Our estimate of the activity duration is based on average skilled engineer. We may get a higher or lower skilled engineer assigned to the activity, causing the actual duration to vary from the planned duration.
7
The accuracy of single-point duration estimates
• The accuracy of single-point duration estimates may be improved by considering estimation uncertainty and risk.
8
Bottom-up estimating
• Bottom-up estimating is a method of estimating project duration or cost by aggregating the estimates of the lower level components of the WBS.
• Using three-point estimates helps define an approximate range for an activity’s duration:
– Most likely (tM). This estimate is based on the duration of the activity, given the resources likely to be assigned.
• When an activity’s duration cannot be estimated with a reasonable degree of confidence, the work within the activity is decomposed into more detail.
• The key benefit of this process is that it generates a schedule model with planned dates for completing project activities.
• Developing an acceptable project schedule is an iterative process.