Who complains? A nationwide register-based cross-sectional study of socioeconomic differences in patient complaints and complaint case outcomes in Denmark

OBJECTIVE: To examine socioeconomic and demographic differences in who complains about healthcare and whether these factors are associated with the outcomes of complaint cases. DESIGN: Nationwide cross-sectional study in Denmark using linked national health, complaint and administrative registers. SETTING: The Danish healthcare system provides universal coverage and has a centralised system for handling complaints with linked patient-level data to sociodemographic variables. PARTICIPANTS: All healthcare contacts in 2022 in general practice (GP), non-psychiatric hospitals and psychiatric hospitals were included. PRIMARY AND SECONDARY OUTCOME MEASURES: We examined two outcomes: (1) submission of a complaint and (2) whether the authorities upheld the complaint. We then assessed how these outcomes varied by socioeconomic position (SEP), focusing on the contrast between patients with the lowest and highest SEP profiles. Relative risks (RRs) were estimated using modified Poisson regression with cluster-robust variance estimation at the patient level. RESULTS: There were 31.9 million GP contacts, 4.8 million non-psychiatric hospital contacts and 345 000 psychiatric contacts, with 1381, 3545 and 439 complaints, respectively (0.43-12.7 per 10 000 contacts). Clear socioeconomic disparities emerged. Low-income patients were more likely to complain about GP and non-psychiatric hospitals, while higher education was associated with fewer complaints in these settings but more complaints about psychiatry. Patients outside the workforce were more likely to complain, whereas elderly patients were consistently underrepresented in the complaints.Low-SEP profiles had notably higher complaint probabilities than high-SEP profiles in GP (RR 2.60, 95% CI 2.22 to 3.70) and non-psychiatric hospitals (RR 1.69, 95% CI 1.40 to 1.98), but not in psychiatric hospitals (RR 0.93, 95% CI 0.47 to 1.38). Although individual SEP indicators showed no consistent differences in complaint outcomes, the combined SEP profiles revealed lower probabilities for complaints being upheld in lower SEP patients in GP (RR 0.58, 95% CI 0.22 to 0.94) and non-psychiatric hospitals (RR 0.70, 95% CI 0.43 to 0.96), while the estimate for psychiatric hospitals was inconclusive (RR 0.71, 95% CI 0.24 to 1.66). CONCLUSIONS: In this nationwide study, socioeconomic and demographic factors were linked to clear differences in both complaint submission and complaint outcomes. Except for psychiatric hospital services, patients with fewer socioeconomic resources were more likely to file a complaint yet had a lower probability of having it upheld. These findings point to disparities in who complains and in how complaints are assessed, and they underline the need to consider all complaints, regardless of outcome, when using complaint data to inform quality improvement efforts.