Relative Estimation
Relative Estimation is an approach used for gauging the complexity, effort, or size of new tasks or items by comparing them to existing tasks or benchmark items. Unlike absolute estimation methods, which assign a specific unit of time or cost to tasks, relative estimation operates by comparing tasks to each other.
Core Concepts
Benchmarking: Initially, a team selects one or more benchmark items that everyone understands well. These benchmarks serve as a reference point against which other items are compared.
Comparison: New backlog items are compared to these benchmarks to determine their relative size or complexity. They might be considered 'twice as complex' or 'half as complex' as the benchmark.
Units: The units used in relative estimation are often arbitrary (e.g., story points, t-shirt sizes) and are valuable only when used for comparison within the same project or team.
Team Agreement: The team collectively agrees on the estimates, often through techniques such as Planning Poker, to arrive at a consensus.
Refinement: As more is learned about the work or as actual data becomes available, estimates may be revisited and revised.
How It Differs from Analogous Estimation
Analogous Estimation: Primarily relies on historical data from past similar projects. It's often a top-down estimation method and usually expressed in absolute units like days or dollars.
Relative Estimation: Does not necessarily require historical data and is typically a bottom-up estimation technique. It uses arbitrary units and relies more on team consensus.
Benefits
Speed: Because it doesn't require detailed analysis or decomposition of tasks, relative estimation is usually faster than other methods.
Flexibility: It accommodates changes more easily, as you only need to reconsider the relative sizes of items, not their absolute estimates.
Collaboration: The method encourages team members to discuss and arrive at a consensus, enhancing team understanding of each item.
Less Error-Prone: By avoiding the complexities associated with deriving absolute values, relative estimation is often less susceptible to major inaccuracies.
Limitations
Calibration: It might take time for a team to become proficient in estimating relatively.
Context-Specific: The estimates are generally not transferable across different teams or projects as they are context-specific.
Applications
Most commonly used in Agile methodologies, such as Scrum and Kanban, for product backlog refinement.
Useful in environments where the work is complex and the scope is not easily decomposed into detailed components.
In summary, Relative Estimation is an effective technique for quickly estimating tasks or backlog items based on their complexity relative to a known benchmark. It fosters team collaboration and is particularly useful in Agile or rapidly changing environments.