Directed Acyclic Graphs in Surgical Research

Published:August 29, 2022DOI:


      Surgical research often utilizes multivariable regression to evaluate causal relationships between variables, but there is usually little explanation of the decision-making regarding which variables were controlled for. We propose that directed acyclic graphs (DAGs)—a formal logic tool that illustrates connections between variables—should be used to define and communicate variable relationships to readers and other audiences. While literature in epidemiology and other medical fields has recently started to incorporate DAGs more, they are still seldom seen in surgical publications. In this review, we describe the background and need for DAGs and argue for their use. Next, we explain how bias can be introduced without a thoughtful approach to control variable selection. Finally, we recommend that researchers communicate their choices and rationale when selecting control variables in published surgical research.


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        • VanderWeele T.J.
        Principles of confounder selection.
        Eur J Epidemiol. 2019; 34: 211-219
        • Hernan M.A.
        The C-word: scientific euphemisms do not improve causal inference from observational data.
        Am J Public Health. 2018; 108: 616-619
        • Murray E.J.
        • Caniglia E.C.
        • Petito L.C.
        Causal survival analysis: a guide to estimating intention-to-treat and per-protocol effects from randomized clinical trials with non-adherence.
        Res Methods Med Health Sci. 2021; 2: 39-49
        • Mansournia M.A.
        • Higgins J.P.T.
        • Sterne J.A.C.
        • Hernán M.A.
        Biases in randomized trials.
        Epidemiology. 2017; 28: 54-59
        • Lipsky A.M.
        • Greenland S.
        Causal directed acyclic graphs.
        JAMA. 2022; 327: 1083-1084
        • Cole S.R.
        • Platt R.W.
        • Schisterman E.F.
        • et al.
        Illustrating bias due to conditioning on a collider.
        Int J Epidemiol. 2010; 39: 417-420
        • Park Y.
        • Peterson L.L.
        • Colditz G.A.
        The plausibility of obesity paradox in cancer.
        Cancer Res. 2018; 78: 1898-1903
        • del Junco D.J.
        • Bulger E.M.
        • Fox E.E.
        • et al.
        Collider bias in trauma comparative effectiveness research: the stratification blues for systematic reviews.
        Injury. 2015; 46: 775-780
        • Greenland S.
        • Pearl J.
        • Robins J.
        Causal diagrams for epidemiologic research.
        Epidemiology. 1999; 10: 37-48
        • Westreich D.
        • Greenland S.
        The table 2 fallacy: presenting and interpreting confounder and modifier coefficients.
        Am J Epidemiol. 2013; 177: 292-298
        • Shrier I.
        • Platt R.W.
        Reducing bias through directed acyclic graphs.
        BMC Med Res Methodol. 2008; 8: 1-15
        • Tennant P.W.G.
        • Murray E.J.
        • Arnold K.F.
        • et al.
        Use of directed acyclic graphs (DAGs) to identify confounders in applied health research: review and recommendations.
        Int J Epidemiol. 2020; 50: 620-632
        • Gaskell A.L.
        • Sleigh J.W.
        An introduction to causal diagrams for anesthesiology research.
        Anesthesiology. 2020; 132: 951-967
        • Williamson E.J.
        • Aitken Z.
        • Lawrie J.
        • Dharmage S.C.
        • Burgess J.A.
        • Forbes A.B.
        Introduction to causal diagrams for confounder selection.
        Respirology. 2014; 19: 303-311
        • Suttorp M.M.
        • Siegerink B.
        • Jager K.J.
        • Zoccali C.
        • Dekker F.W.
        Graphical presentation of confounding in directed acyclic graphs.
        Nephrol Dial Transplant. 2015; 30: 1418-1423
        • Sung V.W.
        Reducing bias in pelvic floor disorders research: using directed acyclic graphs as an aid.
        Neurourol Urodyn. 2012; 31: 115-120
        • Fleischer N.L.
        • Diez Roux A.V.
        Using directed acyclic graphs to guide analyses of neighbourhood health effects: an introduction.
        J Epidemiol Community Health. 2008; 62: 842-846
        • Shackelford S.A.
        • del Junco D.J.
        • Powell-Dunford N.
        • et al.
        Association of prehospital blood product transfusion during medical evacuation of combat casualties in Afghanistan with acute and 30-day survival.
        JAMA. 2017; 318: 1581-1591
        • Gongola A.
        • Bradshaw J.C.
        • Jin J.
        • et al.
        Retrospective study on rib fractures: smoking and alcohol matter for mortality and complications.
        Trauma Surg Acute Care Open. 2021; 6: e000732
        • Sittivarakul W.
        • Prapakornkovit V.
        • Jirarattanasopa P.
        • Bhurayanontachai P.
        • Ratanasukon M.
        Surgical outcomes and prognostic factors following vitrectomy in acquired immune deficiency syndrome patients with cytomegalovirus retinitis-related retinal detachment.
        Medicine. 2020; 99: e22889
        • Bours M.J.L.
        A nontechnical explanation of the counterfactual definition of confounding.
        J Clin Epidemiol. 2020; 121: 91-100
        • Höfler M.
        Causal inference based on counterfactuals.
        BMC Med Res Methodol. 2005; 5: 28
        • VanderWeele T.J.
        • Robinson W.R.
        On the causal interpretation of race in regressions adjusting for confounding and mediating variables.
        Epidemiology. 2014; 25: 473-484
        • Grunvald M.W.
        • Underhill J.M.
        • Skertich N.J.
        • et al.
        Mediating factors between race and time to treatment in colorectal cancer [e-pub ahead of print].
        Dis Colon Rectum. 2021;
        • Waddy S.P.
        • Solomon A.J.
        • Becerra A.Z.
        • et al.
        Racial/ethnic disparities in atrial fibrillation treatment and outcomes among dialysis patients in the United States.
        J Am Soc Nephrol. 2020; 31: 637-649
        • Becerra A.Z.
        • Chan K.E.
        • Eggers P.W.
        • et al.
        Transplantation mediates much of the racial disparity in survival from childhood-onset kidney failure.
        J Am Soc Nephrol. 2022; 33: 1265-1275