Trends and patterns in research and development expenditures in the United States

This paper is a review of recent trends in United States expenditures on research and development (R&D). Real expenditures by both the government and the private sector increased rapidly between the mid-1970s and the mid-1980s, and have since leveled off. This is true of both overall expenditures and expenditures on basic research, as well as funding of academic research. Preliminary estimates indicate that about $170 billion was spent on R&D in the United States in 1995, with ≈60% of that funding coming from the private sector and about 35% from the federal government. In comparison to other countries, we have historically spent more on R&D relative to our economy than other advanced economies, but this advantage appears to be disappearing. If defense-related R&D is excluded, our expenditures relative to the size of the economy are considerably smaller than those of other similar economies.

Sources of selection bias in evaluating social programs: An interpretation of conventional measures and evidence on the effectiveness of matching as a program evaluation method

This paper decomposes the conventional measure of selection bias in observational studies into three components. The first two components are due to differences in the distributions of characteristics between participant and nonparticipant (comparison) group members: the first arises from differences in the supports, and the second from differences in densities over the region of common support. The third component arises from selection bias precisely defined. Using data from a recent social experiment, we find that the component due to selection bias, precisely defined, is smaller than the first two components. However, selection bias still represents a substantial fraction of the experimental impact estimate. The empirical performance of matching methods of program evaluation is also examined. We find that matching based on the propensity score eliminates some but not all of the measured selection bias, with the remaining bias still a substantial fraction of the estimated impact. We find that the support of the distribution of propensity scores for the comparison group is typically only a small portion of the support for the participant group. For values outside the common support, it is impossible to reliably estimate the effect of program participation using matching methods. If the impact of participation depends on the propensity score, as we find in our data, the failure of the common support condition severely limits matching compared with random assignment as an evaluation estimator.