Restricted cubic splines in observational studies exploring the relationship between continuous exposures and risks of cardiometabolic diseases: a methodological survey

Cardiometabolic diseases (CMDs), a group of interconnected disorders mainly including type 2 diabetes mellitus (T2DM), ischemic heart disease (IHD) and stroke, are well-known as the leading cause of death globally. To control the escalating disease burden of CMDs, observational studies assessing the relationship between exposures and risks of CMDs are being increasingly published to help with new targets identification and diseases prevention. Among them, the use of restricted cubic splines (RCS) is widely used to depict the association between continuous exposures and outcomes. However, the methodological quality of its use remains unclear in observational studies, potentially challenging the validity and generalizability of findings from RCS.