This paper reports the results of a statistical summary of estimates of the marginal willingness to pay (MWTP) for reducing particulate matter from hedonic property value models developed between 1967 and 1988. Results using both ordinary least squares and minimum absolute deviation estimators suggest that market conditions and the procedures used to implement the hedonic models were important to the resulting MWTP estimates. The interquartile range for these estimated marginal values (measured as a change in asset prices) lies between zero and $98.52 (in 1982-84 dollars) for a one-unit reduction in total suspended particulates (in micrograms per cubic meter). The mean MWTP is nearly five times the median ($109.90 vs. $22.40), suggesting that outliers are important influences to any summary statistics for these estimates.

As Romer and Weitzman emphasized in the 1990s, new ideas are often combinations of existing ideas, an insight absent from recent models. In Kortum's research around the same time, ideas are draws from a probability distribution, and Pareto distributions play a crucial role. Why are combinations missing, and do we really need such strong distributional assumptions to get exponential growth? This paper demonstrates that combinatorially growing draws from standard thin-tailed distributions lead to exponential growth; Pareto is not required. More generally, it presents a theorem linking the max extreme value to the number of draws and the shape of the upper tail for probability distributions.