A SENSITIVITY INDEX FOR FAIR SUPPLIER SELECTION: ASSESSING SMALL MANUFACTURER DISADVANTAGE IN MCDM METHODS

Abstract

Supplier selection is a critical decision-making problem in manufacturing and supply chain management, commonly addressed using Multi-Criteria Decision Making (MCDM) methods. While existing research has focused on improving methodological accuracy and robustness, limited attention has been paid to how criteria weighting influences selection outcomes across supplier categories. In particular, the impact of weighting structures on small suppliers remains insufficiently understood.This study introduces the Small Supplier Sensitivity Index (SSSI), a diagnostic metric that quantifies the sensitivity of supplier rankings to changes in evaluation priorities. Unlike traditional sensitivity analysis approaches that assess overall ranking stability, the proposed index captures ranking shifts experienced specifically by small suppliers under alternative weighting scenarios. The methodology is implemented using two widely adopted MCDM methods, Simple Additive Weighting (SAW) and TOPSIS, and evaluated through both a real-world supplier dataset and a controlled hypothetical scenario. Results from the real-world case indicate no change in ranking positions for small suppliers under adjusted weighting conditions, yielding an SSSI value of 0 and demonstrating strong structural stability. In contrast, the hypothetical scenario produces a positive SSSI value (SSSI = 2), with small suppliers improving in ranking when greater emphasis is placed on flexibility and reliability. These findings show that the sensitivity of supplier selection outcomes is highly dependent on the distribution of supplier performance, with weighting adjustments having limited impact in highly differentiated environments but significant influence in competitive settings. The proposed framework extends the role of sensitivity analysis in MCDM from model validation to interpretive insight, providing decision-makers with a transparent tool to understand how evaluation priorities shape procurement outcomes. This contributes to more informed and context-aware supplier selection, particularly in environments where fairness and strategic alignment are of interest.