  A recent literature contends that the returns to research in medicine are
declining. This conclusion is premised on two empirical findings: the quantity
of medical research is rising, while improvements in health outcomes are
stagnant. We argue that the first finding is an artifact of conceptual and
empirical problems in the measurement of research. We propose a method for
annotating unstructured text based on fine-tuning a large language model. We
apply this method to construct a census of published clinical trials. We argue
that clinical trials function as a natural proxy for productivity-relevant
research in medicine. In our data, the quantity, quality, and composition of
clinical trials have been stable since 2010. We find that measured increases in
the total quantity of medical research are driven by shifts in the composition
of scientific publications that do not correspond to real increases in the
quantity of productivity-relevant research. We document large increases in the
growth of non-trial publications, driven by publications from China and
publications that review existing literature. This increase in quantity is
coincident with a decline in various measures of average publication quality.
Taken together, we find no support for declining medical research productivity
over this period.
