Endogenous Growth Theory

framework · economics · organizing-schema

Romer and Lucas: technological progress as outcome of economic activity, not exogenous.

Endogenous growth theory, developed principally by Paul Romer and Robert Lucas in the late 1980s, addresses the central limitation of the Solow model by treating the rate of technological progress as the outcome of investment decisions rather than an exogenous parameter. Romer's R&D-based models (1986 increasing-returns variant, 1990 explicit-R&D variant) treat ideas as nonrival goods that generate increasing returns at the aggregate level even where individual firms face constant returns, with deliberate investment in research producing new ideas in equilibrium. Lucas's human-capital approach (1988) emphasizes investment in human capital with positive externalities. The framework rationalizes R&D and education subsidies, predicts that policies affecting innovation can have permanent (not just transitional) growth effects, and earned Romer the 2018 Nobel jointly with William Nordhaus.

Originators

Paul Romer (R&D-based variants); Robert Lucas (human-capital variant) high

Year / Decade

1986 (Romer increasing returns); 1988 (Lucas); 1990 (Romer explicit R&D); 2018 Nobel (Romer) high

Primary sources

Romer, P.M. (1986). 'Increasing Returns and Long-Run Growth', Journal of Political Economy, Lucas, R.E. (1988). 'On the Mechanics of Economic Development', Romer, P.M. (1990). 'Endogenous Technological Change', Journal of Political Economy high

Core components

Nonrival ideas with increasing returns
Deliberate R&D investment producing technological progress
Human capital accumulation with externalities
Knowledge spillovers
AK models (constant marginal product of capital)
Intermediate-goods variety as growth driver
Schumpeterian quality-ladder variants (Aghion-Howitt)

Primary use case

Growth policy analysis (R&D subsidies, education investment, intellectual property design); explanation of permanent rather than transitional effects of growth-relevant policies; analytical foundation for innovation economics; framework for cross-country growth empirics.

Common criticisms

First-generation models exhibit scale effects (larger populations should grow faster) that conflict with empirical evidence — Charles Jones's critique drove a generation of revisions
difficulty measuring ideas and innovation empirically
calibration challenges
structural details (nature of R&D production function, scope of spillovers) are contested
some variants (AK models) have been criticized as relabeled exogenous growth.

Lineage

Child of: Solow Growth Model
Siblings: Solow Growth Model
Derived from: Solow Growth Model