Household Size, Demographic Composition, and per Capita Expenditure: Evidence from Binh Dinh Province, Vietnam

Per capita household expenditure is widely used to assess realized welfare. However, its variation may reflect not only income differences but also household scale, demographic composition, health-related burdens, and social disadvantage. This study examines the conditional correlates of per capita household expenditure in Binh Dinh Province, Vietnam, with particular attention to household size, demographic composition, illness burden, and ethnic-minority status. Using cross-sectional survey data from 320 households collected in 2025, this study estimates a log-linear ordinary least squares (OLS) model and applies bias-corrected and accelerated (BCa) bootstrap inference based on 2000 replications. The results show a strong but less-than-proportional expenditure–income association, with an estimated income elasticity of 0.687. Household size is nonlinearly associated with expenditure, indicating scale advantages at smaller household sizes and resource dilution beyond a threshold. A higher child share and the presence of severe or chronic illness are positively associated with expenditure, whereas elderly and female shares are not statistically significant. Ethnic-minority status remains negatively associated with expenditure after controlling for income, household composition, illness burden, and locational characteristics. These findings show that per capita household expenditure in a developing provincial economy is jointly related to income, household scale, demographic needs, health-related financial pressure, and social vulnerability.