See, also Huffman and Evenson (1989). Alston, Craig, and Pardey (1998) discussed the issue of knowledge depreciation drawing on the previous literature and these arguments are restated and refined by Alston, Pardey, and Ruttan (2008), and Alston, Andersen, James and Pardey (2010). After dropping some outliers and incomplete observations, they conducted regression analysis using a sample of 1 128 estimates with a mean of 64.6%, a mode of 28%, and a median of 42.0%. They found results that were generally consistent with expectations but in many cases they could not distinguish statistically significant effects on the estimated rates of return associated with the nature of the research being evaluated, the industry to which it applied, or the evaluation methodology, because the signal-to-noise ratio was too low. Nevertheless, a predominant and persistent finding across the studies was that the rate of return was quite large. The main mass of the distribution of internal rates of return reported in the literature is between 20% and 80% per annum.