RESUMO
INTRODUCTION To provide equal access, health care provision should be distributed across geodemographic space based on need. In Argentina, the social security, publicly funded health care and private health care subsectors are responsible for delivering health services. In the public subsector, which is responsible for providing primary and secondary care mainly to the uninsured population, supply of services is not always associated with need. The lack of coordination between levels and subsectors makes it difficult to transform need into demand. OBJECTIVE Design a methodology to systematically estimate need, demand and supply of primary health care services based on secondary data sources in order to assess potential mismatches in any geographical area. METHODS An ecological analysis was conducted based on outpatient visits in primary care in Bahía Blanca, Buenos Aires Province, Argentina. A mathematical approach was proposed to systematize data collection by census tract regarding estimated need (number of outpatient visits needed, by specialty, according to age- and sex-specific care protocols and the area's demographics), demand (actual outpatient visits by specialty in each primary health care center), and supply (visit capacity or available appointment slots, taking into account number of personnel hours worked, by specialty). RESULTS Demand for outpatient visits exceeded need (299,731) by 24% while available visit capacity (993,903) could have covered more than twice the number demanded (370,881). Analysis of the three variables grouped by area found that supply correlated more closely with demand (ρ = 0.90) than with need (ρ = 0.68), while spatial analysis showed that supply distribution responded to need. Areas with greater need had a health facility relatively close by, although supply was often located in areas of lower need, and some areas struggle with relatively high need and insufficient supply. CONCLUSIONS Results suggest the need for some reconfiguration of primary health care in the study area. The proposed mechanism for estimating relationship among supply, demand and need is a useful tool to support decision-making. KEYWORDS Health services needs and demand, access to health care; health care accessibility, health care quality, access, and evaluation, health care inequalities, primary health care, Argentina.