This article presents a systematic procedure for constructing a frailty index, which measures the accumulation of health deficits in older adults. The study uses data from the Yale Precipitating Events Project, a cohort of 754 non-disabled individuals aged 70 years or older. The authors describe the selection of health variables as candidate deficits, the recoding of these variables to a 0-1 scale, and the combination of individual deficit scores into a frailty index. The frailty index values follow a gamma distribution, with a rate of deficit accumulation of 0.020 per year at baseline and 0.026 per year at follow-up. The 99% limit to deficit accumulation was 0.6 at baseline and 0.7 at follow-up. Multivariate Cox regression analysis showed that the frailty index, age, and sex were significant predictors of mortality. The method's reproducibility and ability to predict adverse outcomes make it a valuable tool for understanding frailty-related health characteristics in older adults.This article presents a systematic procedure for constructing a frailty index, which measures the accumulation of health deficits in older adults. The study uses data from the Yale Precipitating Events Project, a cohort of 754 non-disabled individuals aged 70 years or older. The authors describe the selection of health variables as candidate deficits, the recoding of these variables to a 0-1 scale, and the combination of individual deficit scores into a frailty index. The frailty index values follow a gamma distribution, with a rate of deficit accumulation of 0.020 per year at baseline and 0.026 per year at follow-up. The 99% limit to deficit accumulation was 0.6 at baseline and 0.7 at follow-up. Multivariate Cox regression analysis showed that the frailty index, age, and sex were significant predictors of mortality. The method's reproducibility and ability to predict adverse outcomes make it a valuable tool for understanding frailty-related health characteristics in older adults.