Human Capital Theory and Adult Education Investment Returns in Nigeria’s Informal Economy

This study examined the applicability and limitations of human capital theory for understanding adult education investment returns within Nigeria's informal economy, developing a conceptual and empirical critique of orthodox human capital frameworks through original research across informal economy workers in Lagos, Kano, and Onitsha. Human capital theory's foundational assumption that education investments generate predictable individual economic returns has been extensively debated in formal labour market contexts, but its application to informal economy adult education investments in sub-Saharan African contexts remains theoretically underdeveloped. The study employed an embedded mixed methods design combining a quantitative survey of 600 informal economy workers (200 per city) measuring adult education participation and economic outcome indicators, with qualitative case studies involving 36 purposively selected workers tracing detailed educational and livelihood trajectories. Quantitative analysis confirmed a statistically significant but modest average rate of return to adult education investments in the informal economy, markedly lower than formal sector education-income relationships. Qualitative findings revealed that returns were highly mediated by social capital networks, access to informal finance, and market structure conditions largely absent from orthodox human capital models. The study develops an original Socially Embedded Human Capital Framework that integrates network and structural factors into human capital return analysis in informal economy contexts. This framework offers a theoretically superior model for understanding adult education investment in Nigeria's informal economy and provides policy evidence for designing socially complementary adult education interventions. Keywords: human capital theory, adult education, informal economy, investment returns, Nigeria.