Validation of the consistency of the frailty index with the frailty phenotype in both males and females across age groups: evidence from the two waves survey of the KLoSA

To date, the two most commonly used methods for evaluating frailty in clinical trials or research are the frailty index (FI) and frailty phenotype (FP). However, the predictive accuracy of these methods across different countries and regions remains controversial. Therefore, the present study analyzed the consistency between these two frailty measurement tools based on the KLoSA data. A total of 11,050 respondents who met the KLoSA Wave 7 and 8 survey criteria were included in the study. FI scores and FP scores were created using 61 health-related variables and 5 health-related phenotypes, respectively. The consistency of these two frailty measurement tools was evaluated using the Kappa coefficient. We observed that (1) both FI and FP were right-skewed in the sample, and both increased with age; (2) regardless of which tool was used for the evaluation, females consistently scored higher than males on frailty; (3) the consistency between the two tools was lower, and the percentage of predictive consistency and the Kappa coefficient of them increased with age, whether male or female. These findings might provide supportive evidence for selecting frailty evaluation tools in future clinical research or self-assessment.