Questions: Romer's Endogenous Technological Progress Model

Question 1

In Romer's model, which property of ideas is ESSENTIAL for generating economy-wide increasing returns to scale, even when individual firms face constant returns?

• A. Excludability — patents allow inventors to prevent rivals from using their ideas
• B. Nonrivalry — an idea can be used simultaneously by any number of firms without being depleted
• C. Scarcity — the limited supply of good ideas drives up their price and returns
• D. Embodiment — ideas only generate returns once they are embedded in physical capital

Answer: (B)

Nonrivalry is the key. A blueprint for a better engine can be used by any number of factories at once — using it in one place does not prevent its use elsewhere. This means doubling all rival inputs (labor, capital) while holding the stock of knowledge constant more than doubles output, because knowledge scales with all uses simultaneously. Excludability matters for private incentives (without some ability to profit, no one invests in R&D), but it is nonrivalry that generates the increasing returns. Excludability without nonrivalry — like a physical machine — would not produce economy-wide scale effects.

Question 2

In Romer's model, the decentralized economy underinvests in R&D relative to the social optimum. What is the PRIMARY reason?

• A. Researchers lack sufficient human capital and training to perform cutting-edge R&D
• B. Monopolistic competition in the intermediate sector makes innovation too risky
• C. Inventors cannot capture the full spillover benefits their ideas generate for future researchers who build on existing knowledge
• D. Patents expire too quickly, reducing the present value of future profits below the cost of research

Answer: (C)

The market failure is a knowledge spillover. When a researcher invents a new intermediate good, other researchers can build on that idea — learning from it, improving it, combining it with other ideas. The private inventor captures profits only from their own patent, not from the value they add to the entire knowledge stock. Because the social return to R&D exceeds the private return, less R&D is done than would be socially optimal. This externality provides the core theoretical rationale for public subsidies to research.

Question 3

In Romer's model, monopolistic competition in the intermediate goods sector is necessary for sustained innovation, because it allows inventors to earn positive profits on their patents.

• T. True
• F. False

Answer: True

This is correct, and it represents a key tension in the model. Monopoly power creates efficiency losses (intermediate goods are priced above marginal cost, so the final goods sector uses fewer inputs than it would under perfect competition). But without monopoly profits, inventors have no private incentive to pay the upfront cost of R&D. Romer's model accepts this inefficiency as the price of sustained innovation — perfect competition would drive profits to zero and eliminate R&D investment.

Question 4

In Romer's model, long-run economic growth is ultimately determined by the rate of physical capital accumulation, just as in the Solow model.

• T. True
• F. False

Answer: False

This is the central point of departure from the Solow model. In Solow, long-run growth depends entirely on exogenous technological progress. In Romer, long-run growth is driven by the rate of idea creation — determined by how much human capital the economy allocates to R&D, the productivity of the research sector, and the size of the market. Physical capital accumulation still matters for the level of output, but it is the endogenous innovation rate that determines the long-run growth rate.

Question 5

Why are ideas fundamentally different from physical goods like machines or raw materials, and how does this difference generate increasing returns to scale in Romer's model?

Model answer: Physical goods are rival: a machine used in one factory cannot simultaneously operate in another. Ideas are nonrival: a blueprint, formula, or algorithm can be used by any number of producers simultaneously without being depleted. This means that when an economy doubles its physical inputs (labor, capital), output more than doubles if the stock of knowledge also grows — because knowledge scales with every use at once. In Romer's model, knowledge accumulates as R&D produces new blueprints for intermediate goods. More variety of inputs raises total factor productivity, so growth can continue indefinitely without running into diminishing returns, unlike in models with only rival inputs.

The nonrivalry of ideas is the engine of the Romer model. It is what makes the aggregate production function exhibit increasing returns, what makes sustained growth possible without exogenous technological manna, and what creates the market failure (spillovers) that justifies R&D subsidies. The model's central message is that growth is not an accident of nature but a consequence of purposeful human investment in knowledge — and that competitive markets left to themselves will systematically underinvest in it.