Blindfolded monkeys or financial analysts: who is worth your money? New evidence on informational inefficiencies in the U.S. stock market

TL;DR

This paper assesses the inefficiency of the U.S. stock market using confidence intervals, finding that a significant proportion of stocks are inefficient, thus supporting the idea that financial analysts outperform random selection.

Contribution

It introduces a novel statistical approach using confidence intervals for proportions to evaluate market inefficiency in the S&P 500.

Findings

Estimated 12.13% to 27.87% of stocks are inefficient.

Supports the view that financial analysts outperform random stock selection.

Provides empirical evidence against the perfect efficiency hypothesis.

Abstract

The efficient market hypothesis has been considered one of the most controversial arguments in finance, with the academia divided between who claims the impossibility of beating the market and who believes that it is possible to gain over the average profits. If the hypothesis holds, it means, as suggested by Burton Malkiel, that a blindfolded monkey selecting stocks by throwing darts at a newspaper's financial pages could perform as well as a financial analyst, or even better. In this paper we use a novel approach, based on confidence intervals for proportions, to assess the degree of inefficiency in the S&P 500 Index components concluding that several stocks are inefficient: we estimated the proportion of inefficient stocks in the index to be between 12.13% and 27.87%. This supports other studies proving that a financial analyst, probably, is a better investor than a blindfolded monkey.