Background Resourcing General Practice (GP) proportionate to need is paramount to delivering equitable, cost-effective care. Approximately half of funding follows a capitation model (the Carr-Hill formula), where patient demographics drive calculations of funding. Previous research has called for funding to be adjusted for socioeconomic data. This study aims to assess whether adjusting either the Carr-Hill formula, or total GP funding, by an area’s deprivation score (Index of Multiple Deprivation (IMD)), leads to a more accurate measure of clinical need.

Methods This cross-sectional study utilised data from 32,844 Lower-Super-Output-Area (LSOA) in England in 2021-2022. Data was obtained from the Office for National Statistics, and NHS Digital. Weighted average Carr-Hill Index (CHI) and total GP funding were calculated for each LSOA using the number of patients registered at each GP surgery per LSOA. IMD and median age were also obtained. Five outcome measures of clinical need were calculated: Combined Morbidity Index (CMI), predicted total morbidity (including undiagnosed morbidity), emergency department (ED) presentations, total GP appointments and age and sex standardised mortality rates (SMR). For both CHI and GP funding, three sets of generalised linear models were calculated for each outcome variable: 1. unadjusted; 2. age-adjusted; and 3. age and IMD adjusted. Adjusted R² value assessed how accurately each model predicted variations in outcome variables. If R² values increased after adjusting for IMD and age (model 3) compared to age alone (model 2), this would indicate that adjusting funding for IMD results in a more accurate measure of clinical need.

Results In age-adjusted models, CHI most accurately predicted CMI (R²=62%), followed by total morbidity (R²=47%). CHI moderately predicted ED admissions and GP appointments (R²=40%, 29%) and poorly predicted SMR (R²=9%). The introduction of IMD enhanced accuracy of all models, most notably for mortality (R²=63%, 49%, 41%, 29%, and 23% respectively). Total-funding showed less robust predictive power for clinical need measured by CMI (R²=47%), total-morbidity (R²=30%), ED admissions (R²=30%), and SMR (R²=9.8%), but stronger for GP appointments (R²=33%). Adjusting for IMD resulted in larger R² increases in all outcomes (R²=53%, 39%, 32%, 23%, and 35% respectively). Pre-pandemic sensitivity-analysis confirmed findings

Discussion These results offer the most compelling evidence to date that incorporating IMD within the Carr-Hill formula, and especially within total-funding, would result in a more accurate funding distribution in relation to need. Total-funding’s lower predictive accuracy for clinical need indicates inefficiencies introduced by pay-for-service and pay-for-performance mechanisms and supports broader use of capitation models. Capitation formulas should better account for variations in mortality.