Causal diagrams that represent three possible relationships between smoking, ESRD, and albumin-to-creatinine ratio (ACR) in the Study of Heart and Renal Protection. Causal diagrams that represent three possible relationships between smoking, ESRD, and albumin-to-creatinine ratio (ACR) in the Study of Heart and Renal Protection. (A) ACR is an effect mediator on the causal pathway between smoking and ESRD. (B) ACR is a collider on one the paths between smoking and ESRD. (C) ACR is an effect mediator on one path and a collider on another path between smoking and ESRD. Natalie Staplin et al. CJASN 2017;12:546-552 ©2017 by American Society of Nephrology