The predictability of rates of return on gold and silver are examined. Econometric tests do not reject the martingale hypothesis for either asset. This failure to reject is shown to be misleading. Correlation dimension estimates indicate a structure not captured by ARCH. The correlation dimension is between 6 and 7 while the Kolmogorov entropy is about 0·2 for both assets. The evidence is consistent with a nonlinear deterministic data generating process underlying the rates of return. The evidence is certainly not sufficient to rule out the possibility of some degree of randomness being present.

We explore the importance of modeling strategies when estimating the emissions-income relationship. Using U.S. state-level panel data on nitrogen oxide and sulfur dioxide emissions, we estimate several environmental Kuznets curves using the standard parametric framework as well as a more flexible semiparametric alternative. Formal statistical comparisons of the results overwhelmingly reject the parametric approach. Moreover, the differences, particularly for sulfur dioxide, are economically significant.