As shown in the meta-analysis by Alston et al. ( In particular, measures of agricultural inputs (especially capital), outputs, and productivity, are very much transformed from the raw material used to make them. Studies of the returns to agricultural R&D, involve significant further transformation of data on research investments and productivity that already had embodied in them a great deal of judgment, much of which may not be apparent to the user but can have important implications for findings from studies that use them.