What is the fundamental difference between the Solow growth model and endogenous growth models in explaining long-run per-capita growth?
ASolow assumes diminishing returns to capital while endogenous models assume constant returns, but both treat technology as fixed
BSolow treats long-run growth as driven by a technology parameter that falls outside the model, while endogenous models generate sustained growth from within the economic system through innovation, human capital, or knowledge spillovers
CSolow focuses on physical capital while endogenous models focus exclusively on labor force growth
DEndogenous models require government intervention to sustain growth while Solow shows growth is self-sustaining without policy
In the Solow model, long-run per-capita growth depends entirely on the exogenous rate of technological progress (A-dot/A), which the model takes as given and cannot explain. Without this exogenous input, Solow predicts the economy converges to a steady state with zero per-capita growth. Endogenous growth models close this gap by modeling technology, human capital, or knowledge as outputs of economic decisions — investment in R&D, education, or learning-by-doing — so that policy and incentives directly affect the long-run growth rate.
Question 2 True / False
In endogenous growth models, government policy such as education subsidies or R&D tax credits can permanently raise the long-run per-capita growth rate.
TTrue
FFalse
Answer: True
This is precisely the distinguishing feature of endogenous growth theory. Because growth is generated by mechanisms inside the model — human capital accumulation, knowledge production, spillovers — policies that affect those mechanisms can permanently change the growth rate, not just the level of output. In Solow, by contrast, policy can raise the level of the growth path (e.g., a higher saving rate shifts the steady-state capital stock) but cannot change the long-run growth rate, which is fixed by exogenous technology. The policy-responsiveness of growth rates is why endogenous models have major implications for industrial policy and innovation economics.
Question 3 Short Answer
What is a knowledge externality, and why does its presence imply that a market economy will tend to under-invest in R&D relative to the social optimum?
Think about your answer, then reveal below.
Model answer: A knowledge externality occurs when the benefits of a new idea or innovation spill over to other firms or workers beyond the innovator, who cannot fully capture those benefits through prices or patents. Because private innovators only receive the private return on their R&D, not the full social return (which includes the spillover benefits), they invest less than would be socially optimal.
Knowledge is a non-rival good: once an idea exists, it can be used by many people simultaneously without depletion. This creates positive externalities — when one firm invests in R&D and its discoveries diffuse to competitors or to the broader knowledge base, society benefits more than the innovating firm can capture in profits. Because the private return to innovation is less than the social return, unregulated markets under-provide R&D and innovation. This is the economic justification for policies like R&D tax credits, public research funding, and intellectual property protection (though IP protection trades off the incentive to innovate against the inefficiency of monopoly pricing on ideas).