Robust shift scheduling with discretionary rest breaks

Shift scheduling is a critical task in workforce management, which consists of covering the staffing needs by feasible work shifts at minimum labor cost. Work shifts must include rest breaks according to national regulations and collective agreements, significantly impacting the expected Level of Service (LoS) provided to the customers. Therefore, managers tend to preserve the LoS by rigidly scheduling breaks at a centralized level. This affects the well-being of employees, who, especially in large organizations, require more discretion in choosing rest breaks to reduce work stress. This paper presents a two-stage robust optimization model with decision-dependent uncertainty to handle discretionary break assignment. This is a challenging problem both in theory and practice. We formulate it as a bilevel program and develop a tailored heuristic algorithm to find high-quality shift schedules for staffing patterns of several service systems. This methodology allows managers to assess the cost of discretion and to finely determine the best trade-off among discretion, LoS, and labor cost.