Overview
Analogous estimation (also called top-down estimation) uses data from similar past projects to estimate the duration, effort, and resources needed for a new project.
How It Works
Process
- Identify similar completed projects
- Review actual time and resources used
- Adjust for differences (size, complexity, team)
- Apply adjusted estimates to new project
- Document assumptions and basis
Requirements
- Historical project data
- Similar project characteristics
- Documented past performance
- Understanding of differences
When to Use
Ideal Scenarios
- Early project phases (limited detail)
- Similar projects to past work
- Quick estimates needed
- High-level planning
- Budget ballpark figures
Less Suitable
- Novel projects (no analogues)
- Highly detailed estimates needed
- Significant differences from past work
- Final budget approval
Advantages
- Fast: Quick to generate estimates
- Low cost: Minimal effort required
- Experience-based: Leverages real data
- Useful early: Works with limited information
- Organizational learning: Builds knowledge base
Disadvantages
- Accuracy varies: Depends on similarity
- Requires history: Needs past project data
- Subjective: Judgment in selecting analogues
- May miss details: Top-down approach
- Bias risk: Pattern matching errors
Best Practices
1. Select True Analogues
- Similar scope and complexity
- Same or similar technology
- Comparable team size and skills
- Similar constraints
- Recent enough to be relevant
2. Adjust for Differences
- Team experience level
- Technology changes
- Scope variations
- Resource availability
- External factors
3. Use Multiple References
- Don't rely on single project
- Average across several analogues
- Weight by similarity
- Consider range of outcomes
4. Document Assumptions
- Which projects used as basis
- What adjustments made
- Why those adjustments
- Confidence level
- Known risks
Integration with Time Tracking
Build Historical Database
- Track all project time
- Categorize by type and characteristics
- Document complexity factors
- Record actual vs. estimated
- Note lessons learned
Improve Estimates Over Time
- Compare analogous estimates to actuals
- Identify systematic bias
- Refine adjustment factors
- Build estimation accuracy
Create Reference Library
- Standard project profiles
- Typical durations by project type
- Complexity multipliers
- Team productivity factors
Common Patterns
By Project Size
- Small: 1-3 months
- Medium: 3-6 months
- Large: 6-12 months
- Enterprise: 12+ months
Adjustment Factors
- Team experience: 0.7-1.3x
- Technology newness: 1.0-2.0x
- Complexity: 0.8-1.5x
- Stakeholders: 1.0-1.4x
Combining with Other Methods
- Analogous + Expert judgment: Validate estimates
- Analogous + Parametric: Use both top-down and model-based
- Analogous + Bottom-up: Reconcile differences
- Analogous + Three-point: Refine range
Example
Past Project: Website redesign, 3 developers, 4 months
New Project: Similar website redesign
- Same technology
- 2 developers (vs. 3)
- More features
Estimate: 4 months × (3/2 team ratio) × 1.2 (more features) = ~7 months
