A negative or nonsignificant empirical correlation between aggregate R&D intensity and the economic growth rate is a well-known fact in the empirical growth literature, but scarcely addressed in the theoretical growth literature. This paper develops an endogenous-growth~model that explores the interrelation~between horizontal and vertical R&D under a lab-equipment specification that is consistent with that stylized fact. A key feature is that the growth rate is fully endogenous both on the intensive and on the extensive margin. Strong composition effects between horizontal and vertical R&D, along both transition and the balanced-growth path, then emerge as the main mechanism producing those results. This setting also allows us to obtain a relationship between economic growth and firm dynamics that is consistent with the empirical facts.
