A Behavioral Model of Stock Market Investors' Impact on Consumption

This paper offers a theory of investor/consumer behavior in the context of an adaptive relationship. It shows how consumer spending and stock market gains and losses interact in a "gradual diffusion" process. The model offers predictions about likely changes in investor behavior, and the impact on the underlying economy in general and consumption in particular. These predictions are validated empirically. Specifically, the paper finds that investors/consumers gradually smooth their "wealth spending" and accelerate consumption as they become more convinced that their gains are permanent. This is somewhat reminiscent of the "income smoothing" suggested by Friedman 1957]. We present evidence that the consumption wealth spending peaks at approximately 2.5%-3% of the stock market wealth cumulative gain in the previous twelve- to twenty-four-month period, while concurrent effects are negligible. The results also provide a partial explanation for the long cycle of a strong economy in the 1990s, and point out the danger to the economy from a prolonged stock market decline.