Variance Bounds Tests and Stock Price Valuation Models
指出先前用股票价格与完美预见价格图来证明过度波动或贴现率非常数的做法无效，因为贴现率不变时完美预见价格比理性价格更平滑；在非平稳条件下，条件方差界对标准普尔数据并未被违反，结果与未来现金流预期变化导致股价变化一致。
Previous use of plots of stock prices and "perfect-foresight" prices p*"t as evidence of either "excess volatility" or nonconstant discount rates is invalid since by construction p*"t will differ form and be much smoother than rational prices if discount rates are constant. Further, prices appear nonstationary, which can account for the previously reported gross violations of variance bounds. Conditional variance bounds that are valid under nonstationarity are not violated for Standard and Poor's data. The results are consistent with changes in expectations of future cash flows causing changes in expectations future cash flows causing changes in stock prices.