Research has shown that patients admitted to the hospital on the weekend may experience worse outcomes compared to those admitted on weekdays (the ‘weekend effect’). This editorial highlights the challenges to empirically evaluate the underlying mechanisms contributing to the weekend effect. The authors propose viewing the weekend effect as a proxy for staffing levels and the influence of other factors influencing outcomes for patients admitted on weekends, such as patient acuity, clinician skill-mix and access to diagnostic tests or other ancillary services.