Pairwise Comparison
Pairwise Comparison is a systematic and analytical prioritization technique used in requirements management to rank requirements by comparing them with each other in pairs. This method involves taking each requirement and comparing it directly against every other requirement to assess which one is more important. The fundamental premise is that it's easier for stakeholders to make a decision between two items rather than across a list of many. In practice, a matrix is often created where requirements are listed both horizontally and vertically. Each cell in the matrix represents a comparison between two requirements. Stakeholders or decision-makers go through the matrix, comparing the pairs, and assigning a value based on which requirement is deemed more important or if they hold equal importance. The values assigned during the comparisons are then tallied for each requirement. The totals are used to rank the requirements from highest to lowest priority. This method ensures a thorough evaluation, as every requirement is directly compared with every other, reducing bias that may occur when evaluating requirements independently. Pairwise Comparison is particularly useful when dealing with a moderate number of requirements. While the technique provides a high degree of precision in prioritization, it can become time-consuming and complex as the number of requirements increases because the number of comparisons grows exponentially. Benefits of Pairwise Comparison include fostering stakeholder engagement and facilitating discussions about the relative importance of requirements. It can reveal differing opinions among stakeholders, providing an opportunity to align on priorities and resolve conflicts. The method also aids in uncovering underlying rationale for preferences, leading to a deeper understanding of business needs. However, limitations include the potential for the process to become unwieldy with large numbers of requirements. It also assumes that all requirements can be directly compared, which may not be the case if they are of different types or relate to different aspects of the project. Despite these challenges, Pairwise Comparison remains a valuable tool for prioritization when used appropriately. By systematically assessing each requirement in relation to others, organizations can ensure that the most critical requirements are identified and addressed first, leading to more effective resource allocation and better alignment with business objectives.
Pairwise Comparison: A Comprehensive Guide for PMI-PBA Exam
Why Pairwise Comparison is Important
Pairwise comparison is a crucial requirements prioritization technique because it provides a systematic and objective method to rank requirements when dealing with multiple stakeholders and competing priorities. It's important because:
• It reduces complex decision-making into manageable, binary choices
• It creates a mathematical basis for prioritization
• It minimizes bias by forcing direct comparisons
• It helps resolve conflicts between stakeholders with different priorities
• It creates documented justification for prioritization decisions
What is Pairwise Comparison?
Pairwise comparison is a structured prioritization technique that evaluates requirements by comparing them two at a time. Each requirement is compared against every other requirement, forcing a choice between pairs. Through these binary comparisons, a complete prioritized list emerges based on how often each requirement was preferred.
This technique is particularly valuable when:
• You need to prioritize a moderate list of requirements (typically 5-20 items)
• Stakeholders disagree about priorities
• You need mathematical justification for decisions
• You want to minimize the impact of dominant personalities
How Pairwise Comparison Works
Step 1: Create your requirements list
Assemble all requirements that need prioritization.
Step 2: Build a comparison matrix
Create a grid with requirements listed in both rows and columns.
Step 3: Perform the comparisons
For each pair, decide which requirement is more important. Enter a '1' in the cell where the row item is preferred over the column item, and '0' when it's not preferred.
Step 4: Calculate the scores
Sum the rows to determine how many times each requirement was preferred over others.
Step 5: Rank the requirements
Arrange requirements in descending order by their scores.
Example:
With requirements A, B, C, and D:
1. Compare A vs B: If A is preferred, enter '1' in row A, column B
2. Compare A vs C: If C is preferred, enter '0' in row A, column C
3. Continue until all pairs are compared
4. Sum each row to get total scores
5. Rank requirements based on these scores
Exam Tips: Answering Questions on Pairwise Comparison
• Recognize the technique: Questions may describe a scenario with paired comparisons rather than explicitly naming the technique.
• Understand the math: For n requirements, there will be n(n-1)/2 comparisons. For 5 requirements, expect 10 comparisons.
• Know the limitations: Pairwise comparison works best with 5-20 items. Too many items make the process cumbersome.
• Calculation questions: Be prepared to identify which requirement ranks highest based on comparison results.
• When to use: Recognize scenarios where pairwise comparison is most appropriate (moderate list size, need for objective ranking).
• Benefits and drawbacks: Understand that while it's thorough and objective, it can be time-consuming.
• Process steps: Remember the sequence of creating the matrix, performing comparisons, and calculating results.
When answering exam questions about pairwise comparison, pay attention to:
• The specific problem being solved (usually prioritization)
• The number of items being compared
• How the results are calculated and interpreted
• The advantages of this technique in the given scenario
Pairwise comparison is frequently tested alongside other prioritization techniques like MoSCoW, Kano Model, and Voting. Make sure you can differentiate when each is most appropriate.
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