Restriction of range effects in post–metabolic and bariatric surgery outcomes research: considerations for clinical decision making

Background: Preoperative psychopathology does not consistently predict postoperative outcomes in patients who undergo metabolic and bariatric surgery (MBS). Individuals with elevated pre-MBS psychopathology may be less likely to undergo surgery, which may create a floor effect given the limited range of scores on measures of psychopathology included in postoperative analyses, thereby decreasing the power to detect clinically significant differences between groups. Objectives: Our objective was to compare rates of clinically significant pre-MBS psychopathology across domains of functioning in patients who did and did not undergo MBS: surgical completers (SCs, n = 286) and nonsurgical completers (NSCs, n = 125). Setting: Academic medical center, United States. Methods: Participants (n = 411) were a racially diverse sample of MBS candidates who completed a preoperative psychosocial evaluation including measures of disordered eating, alcohol and tobacco use, pain catastrophizing, anxiety, and depressive symptomatology. Results: Compared with SCs, NSCs had larger scale score variance on measures of psychopathology and were more likely to be Black; to report clinically significant scores on measures of binge eating, depression, anxiety, and pain catastrophizing; and to use tobacco. Conclusion: Results support the presence of a restriction-of-range effect but do not demonstrate a floor effect. These data suggest that current outcome data for MBS patients may not generalize to those who report clinically significant psychopathology at the pre-MBS psychosocial evaluation and may warrant caution when using the current literature to inform clinical decision making for this group. Findings also suggest a need for interventions that will better engage Black patients.