Small Area Frailty Index

Summary

The Small Area Frailty Index (SAFI) is a population-level measure of frailty, designed to capture the proportion of frail individuals within small geographic areas, such as Middle Super Output Areas (MSOAs). SAFI is available for each year (post 2014), allowing longitudinal analysis of frailty trends.

Technical description

The creation of the Small Area Frailty Index (SAFI) using the Electronic Frailty Index (eFI) framework is based on a cumulative deficit model, which assesses frailty by accounting for the accumulation of various health deficits. First, data is extracted from the Hospital Episode Statistics (HES) database for patients aged 65 and older, including the past four consecutive years of hospital admissions for each individual to ensure comprehensive coverage.

Next, the frailty is calculated for each patient by identifying and flagging 32 health deficits from their recorded hospital admissions. These deficits span chronic diseases, functional impairments, and social vulnerabilities. The Housebound and Polypharmacy deficits have been excluded because they are not available in HES data and 2 deficits (Hypertension/ syncope and Requirement for care) have been combined to existing deficits (Hypertension and Mobility & transfer problems) respectively. The frailty score is computed as the sum of these deficits divided by 32, representing the maximum possible number of deficits.

Once the frailty scores are calculated, they are aggregated at the Middle Super Output Area (MSOA) level to provide a population-based measure of frailty. This aggregation generates the overall SAFI, which reflects the proportion of patients with moderate to severe frailty (eFI > 0.24) across all deficits. Finally, the entire process is repeated annually (post 2014) to enable the analysis of temporal trends in frailty across community levels.