This paper analyzes the impact of US decimalization on the Canadian stocks listed on the Toronto Stock Exchange (TSE) and either the New York Stock Exchange (NYSE) or National Association of Securities Dealers Automated Quotation System (Nasdaq) in the US. Using a sample of 126 firms, we find that the US trading of these stocks increases after decimalization, but this increase is not at the expense of TSE volume. Indeed, the TSE volume increases substantially for those securities that are traded on Nasdaq and increases marginally for those securities that are traded on the NYSE. Most of the increase in volume is in retail-sized trades. The bid–ask spreads and the quote depths decline on all exchanges, but by a greater amount in the US than in Canada. The depths on the NYSE decline from being above the TSE depths to well below the TSE depths. We also find that the decline in the TSE spread is directly related to the size of the firm and to the decline in the US spread, and is inversely related to the pre-decimalization ratio of spreads on the US exchange and the TSE. Overall, our results indicate that the US decimalization had the desired positive impact on trading in both the US and Canada, with a decrease in spreads and an increase in retail-sized trading.

Terry E. Dielman, Henry R. Oppenheimer, An Examination of Investor Behavior During Periods of Large Dividend Changes, The Journal of Financial and Quantitative Analysis, Vol. 19, No. 2 (Jun., 1984), pp. 197-216

In an efficient capital market, prices fully reflect available information and adjust to new information in a rapid and unbiased fashion. As a result, prices provide unbiased estimates of the underlying values. No known trading rule or security selection strategy which uses only publicly available information would provide an investor with the ability to earn, on average, positive “abnormal” returns in a market that is efficient in the semi-strong sense. Thus, a finding that common stocks selected, using a readily available, widely disseminated set of rules which requires only publicly available information for decision-making purposes, earn, on average, positive abnormal returns represents strong contradictory evidence regarding the semi-strong form of the efficient markets hypothesis.