Aggregates By Terry A Marsh

• In a series of stimulating papers (198la, l98lb, and Robert Shiller uses seemingly powerful variance bounds tests to show that variations in aggregate stock market prices are much too large to be justified by the variation in subsequent dividend payments. Under the assumption that the real expected return on the market remains essentially constant over time, Shiller concludes that the excess variation in stock prices identified in his tests provides strong evidence to reject the Efficient Market Hypothesis. Even if the real expected return on the market does change over time, Shiller further concludes that the amount of variation in that rate necessary to save the Efficient Market Hypothesis is so large that the measured excess variation in stock prices cannot be attributed to this source.
• We need hardly mention the significance of such a conclusion. If Shiller's rejection of market efficiency is sustained, then serious doubt is cast on the validity of the most important cornerstone of modern financial economic theory. To be sure, of the hundreds of earlier tests of efficient markets, there have been a few which appear to reject market efficiency [cf.