Convergent validity of the electronic frailty index

Background: the electronic frailty index (eFI) has been developed and validated using routine primary care electronic health record data. The focus of the original big data study was on predictive validity as a form of criterion validation. Convergent validity is a subtype of construct validity and considered a core component of the validity of a test. Objective: to investigate convergent validity between the eFI and research standard frailty measures. Design: cross-sectional validation study using data from the Community Ageing Research 75+ (CARE 75+) cohort. Setting: multi-site UK community-based cohort study. Subjects: three hundred fifty-three community-dwelling older people (median age 80 years, IQR 77-84), excluding care home residents and people in the terminal stage of life. Median eFI score of participants was 0.22 (IQR 0.14-0.31). Methods: convergent validities between the eFI and: a research standard frailty index (FI); the phenotype model of frailty; Clinical Frailty Scale (CFS) and Edmonton Frail Scale were assessed using scatter plots and Spearman's rank tests to estimate correlation coefficients (Spearman's rho, ρ) and 95% confidence intervals. Results: results indicate strong correlation between the eFI and both the research standard FI (ρ = 0.68, 95% CI 0.62-0.74) and Edmonton Frail Scale (ρ = 0.63, 95% CI 0.57-0.69). There was evidence for moderate correlation between the eFI and both the CFS (ρ = 0.59, 95% CI 0.49-0.65) and phenotype model (ρ = 0.51, 95% CI 0.42-0.59). Conclusions: This study provides evidence for convergent validity of the eFI, a core component of test validity.