Other reviews of the literature may not have covered the same studies or in the same ways, but nevertheless reached similar general conclusions—for instance, Evenson (2002), and Fuglie and Heisey (2007). For all characteristics, the sample excludes two extreme outliers and includes returns to research only and combines research and extension so that the maximum sample size is 1 772. For the research gestation lag, the sample includes only observations with an explicit lag shape, resulting in a sample size of 790 observations.