Project Than Time: Relative Estimating for Simplified Planning
PMBOK v8 Definition
Project Than Time is an estimating approach that uses relative size comparisons rather than absolute time, based on the understanding that teams are typically better at comparing work items than predicting precise durations. This approach simplifies planning while preserving accuracy, as estimating hours can be more time-consuming and less reliable in dynamic environments. This concept is part of the Schedule performance domain within the Project Management process groups.
Why It Matters for the Exam
The PMI exam frequently tests this concept in questions about estimating techniques, schedule development, and agile or adaptive approaches. Expect questions that contrast relative estimating (comparing work items) with absolute time estimating (hours/days), particularly in scenarios involving dynamic environments or teams with limited historical data. The exam also tests your understanding of why this approach preserves accuracy while simplifying planning.
Key Points to Remember (for the exam)
- Core Principle: Teams are better at comparing work items than predicting precise durations in hours or days
- Key Benefit: Simplifies planning while preserving accuracy, because estimating hours is more time-consuming and less reliable in dynamic environments
- Primary Application: Used when work items are uncertain, requirements are evolving, or historical data is limited
- Common Technique: Story points, t-shirt sizes, or other relative sizing methods replace absolute time estimates
- Cognitive Bias Awareness: Be aware that planning fallacy and end-of-story illusion can impact estimating accuracy regardless of the method chosen
- Progressive Elaboration: Duration estimates improve as more detailed and precise data become available about project engineering and design work
- Relationship to Resources: Estimating effort and duration requires estimating both work effort AND available resources, then using project and resource calendars to determine work periods
Typical PMI Exam Example
A project team is developing a new software feature but has limited historical data on similar work. The project manager asks the team to estimate using story points rather than hours. Each user story is compared to a baseline story, and the team assigns relative values. This approach is applied because the team is better at comparing work items than predicting precise durations, and estimating hours would be more time-consuming and less reliable in this dynamic environment.
PMI Exam Traps
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Trap: Confusing relative estimating with analogous estimating Reality: Relative estimating compares work items within the same project using a baseline; analogous estimating uses historical data from similar past projects
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Trap: Thinking relative estimating eliminates the need for any time-based planning Reality: Relative estimates still need to be converted to durations using team velocity or historical throughput data for scheduling
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Trap: Assuming relative estimating is only for agile projects Reality: The PMBOK v8 presents this as a general approach applicable when teams are better at comparison than precise prediction, regardless of methodology
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Trap: Believing relative estimating is always more accurate than absolute time estimating Reality: The approach preserves accuracy in dynamic environments but may not be appropriate when regulatory or contractual requirements demand precise time-based estimates
Important PMI Connections
| Related Concept | Relationship Type | Exam Attention Point |
|---|---|---|
| Alternative Analysis | Complementary technique | Alternative analysis evaluates options to select the best approach; relative estimating is one option evaluated during alternative analysis |
| Analogous Estimating | Different approach | Analogous uses past project data; relative comparing uses current project work items against a baseline |
| Duration Estimating | Core process | Relative estimating feeds into duration estimating; effort and duration estimates use resource calendars to determine work periods |
| Cognitive Bias | Risk factor | Planning fallacy and end-of-story illusion impact accuracy of both relative and absolute estimating |
| Progressive Elaboration | Quality factor | As more detailed data becomes available, the accuracy and quality of duration estimates improve |
Quick Review Questions
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According to PMBOK v8, why are teams typically better at comparing work items than predicting precise durations?
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A project manager chooses to use relative estimating instead of hourly estimates for a project with evolving requirements. What is the primary benefit of this approach?
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What cognitive biases does PMBOK v8 identify that may impact the accuracy of the scheduling process, regardless of the estimating method used?
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When converting relative estimates to actual durations, what two types of information must be combined according to the PMBOK v8 estimating process?
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How does the quality and availability of input data affect duration estimates in the context of progressive elaboration?
PMBOK v8 Reference
Section 2.5 - Schedule Performance Domain (Step 3: Estimate Effort and Duration)