A conceptual review of Six Sigma applications in supermarket operations: comparative insights and a framework for sales and inventory optimization

Supermarkets operate in highly competitive, demand-volatile environments where inefficiencies in inventory management, replenishment, and shelf availability directly impact sales and operating costs. To address these challenges, Six Sigma and Lean Six Sigma (LSS) methodologies are increasingly applied in retail operations to improve process stability, reduce variability, and enhance customer performance. This paper presents a comprehensive conceptual review of peer-reviewed studies on Six Sigma and LSS applications in supermarkets, focusing on inventory control, replenishment, stockout reduction, and sales improvement. Using a structured review approach, the literature is systematically classified by process focus, methodological tools, and performance outcomes. Comparative analysis highlights dominant application areas, commonly used tools, operational benefits, and research gaps. Existing studies largely examine inventory or process efficiency separately, with limited integration of customer-facing sales metrics and inventory decision variables. To bridge this gap, the paper proposes a Sales and Inventory Optimisation Framework based on the DMAIC methodology, linking customer quality attributes, operational variables, and economic indicators. The framework offers a structured approach for managers and researchers to jointly optimise sales and inventory efficiency, contributing to theory and practice by consolidating fragmented knowledge and providing a practical roadmap for continuous improvement in supermarket operations.