Using datasets to ascertain the generalizability of clinical cohorts: the example of the European QUALity study on the treatment of advanced chronic kidney disease

Nephrol Dial Transplant. 2022 Feb 25;37(3):540-547. doi: 10.1093/ndt/gfab002.


Background: Cohort studies are among the most robust of observational studies but have issues with external validity. This study assesses threats to external validity (generalizability) in the European QUALity (EQUAL) study, a cohort study of people >65 years of age with Stage 4/5 chronic kidney disease.

Methods: Patients meeting the EQUAL inclusion criteria were identified in The Health Improvement Network database and stratified into those attending renal units, a secondary care cohort (SCC) and a not primary care cohort (PCC). Survival, progression to renal replacement therapy (RRT) and hospitalization were compared.

Results: The analysis included 250, 633 and 2464 patients in EQUAL, PCC and SCC. EQUAL had a higher proportion of men compared with PCC and SCC (60.0% versus 34.8% versus 51.4%). Increasing age ≥85 years {odds ratio [OR] 0.25 [95% confidence interval (CI) 0.15-0.40]} and comorbidity [Charlson Comorbidity Index ≥4, OR 0.69 (95% CI 0.52-0.91)] were associated with non-participation in EQUAL. EQUAL had a higher proportion of patients starting RRT at 1 year compared with SCC (8.1% versus 2.1%; P < 0.001). Patients in the PCC and SCC had increased risk of hospitalization [incidence rate ratio 1.76 (95% CI 1.27-2.47) and 2.13 (95% CI 1.59-2.86)] and mortality at 1 year [hazard ratio 3.48 (95% CI 2.1-5.7) and 1.7 (95% CI 1.1-2.7)] compared with EQUAL.

Conclusions: This study provides evidence of how participants in a cohort study can differ from the broader population of patients, which is essential when considering external validity and application to local practice.

Keywords: EQUAL; THIN; cohort study; external validity; generalizability.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acute Kidney Injury* / etiology
  • Aged, 80 and over
  • Cohort Studies
  • Humans
  • Kidney
  • Male
  • Renal Insufficiency, Chronic* / complications
  • Renal Insufficiency, Chronic* / epidemiology
  • Renal Insufficiency, Chronic* / therapy
  • Renal Replacement Therapy