Project Time Management - Estimate Activity Durations

This process estimates the number of work periods (amount of time) needed to complete individual activities with estimated resources.

Lets take a look at the Inputs, Tools and Techniques, and Outputs of this process.

1) Schedule Management Plan

• Defines the method used and the level of accuracy along with other criteria required 

2) Activity List

• Identifies the activities that will need duration estimates

3) Activity Attributes

• Provides the primary data input for use in estimating durations required for each activity in the activity list

4) Activity Resource Requirements

• This will impact on the duration of the activity depending on the level to which the resources are assigned to the activity

5) Resource Calendars

• Depending on the availability of the resources, type of resources and resources with specific attributes will impact the duration of schedule activities

6) Project Scope Statement

• You will use the assumptions and constraints in the project scope statement to help with activity durations.
• Assumptions - existing conditions, availability of information, and length of reporting periods. 
• Constraints - Available skilled resources, and contract terms and requirements. 

7) Risk Register

• Provides a list of risks along with the results of risk analysis and risk response planning. 

8) Resource Breakdown Structure

• Provides a hierarchical structure of the identified resources by resource category and resource type

9) Enterprise Environmental Factors

• Factors may include:
• Duration estimating databases
• Productivity metrics
• Published commercial information
• Location of team members

10) Organizational Process Assets

• Factors may include:
• Historical duration information
• Project calendars
• Scheduling methodology
• Lessons learned

11) Expert Judgement

• Experts can provide duration estimate information and suggest how to reconcile differences between methods of estimating. 

12) Analogous Estimating

• Technique for estimating the duration or cost of an activity or a project using historical data from a similar activity or project. (duration, budgets, size, weather and complexity) This technique is less costly, less time consuming and less accurate. It is the most reliable when the previous activity is similar to the one in the current project. 

13) Parametric Estimating 

• Technique in which an algorithm is used to calculate cost or duration based on historical data and project parameters. This technique can produce higher levels of accuracy. 

14) Three-Point Estimating

• Technique used to estimate cost or duration by applying an average of optimistic, pessimistic, and most likely estimates when there is uncertainty with the individual activity estimates. 
• It came from the program evaluation and review technique (PERT) that uses three estimates to define an approximate range for an activity's duration
• Most likely (tM) - estimate is based on 
• the duration of the activity
• given the resources likely to be assigned
• resource productivity
• realistic expectations of availability for the activity
• dependencies on other participants
• interruptions
• Optimistic (tO)- based on analysis of best-case scenario for the activity
• Pessimistic (tP) - based on analysis of the worst-case scenario for the activity
• Formulas used to calculate expected duration (tE) 
• Triangular Distribution
• tE = (tO + tM + tP) / 3
• expected duration = (Optimistic + Most likely + Pessimistic) divided by 3
• Beta Distribution
• tE = (tO + 4tM + tP) / 6
• expected duration = (Optimistic + 4 times Most likely + Pessimistic) divided by 6

15) Group Decision Making

• Team-based approaches help improve estimate accuracy and commitment to the emerging estimates.
• Brainstorming
• Delphi - technique for gathering information and used as a way to reach a consensus of experts on a subject. Participants are anonymous through the use of a questionnaire which is then summarized and recirculated for further comment
•  Nominal group techniques - technique that enhances brainstorming with a voting process used to rank the most useful ideas for further brainstorming or for prioritization

16) Reserve Analysis

• Duration estimates may include contingency reserves which are buffers of time scheduled into the project to allow for uncertainty. They can be developed by:
• Percentage of estimated activity duration
• Fixed number of work periods
• Monte Carlo simulation - process which generates hundreds or thousands of probable performance outcomes based on probability distributions for cost and schedule on individual tasks. The outcomes are then used to generate a probability distribution for the project as a whole. 
• Management reserves - amount of time reserved for management of the project and are used to address the unknown- unknowns that affect the project

17) Activity Duration Estimates

• These are quantitative assessments of the likely number of time periods that are required to complete an activity. 
• 2 weeks + or - 2 days (least 8 days and no more than 12 days) 

18) Project Documents Updates

• Documents that you may update includes:
• Activity attributes
• Assumptions made (skill level, availability, estimate durations) 

Source: PMBOK 5th ed.