The second page contains a succinct summary of theoretical reasons why this is true. The rest of the paper goes over empirical findings: <a href="http:&#x2F;&#x2F;www.acsu.buffalo.edu&#x2F;~keechung&#x2F;MGF743&#x2F;Readings&#x2F;G2%20Decimalization.pdf" rel="nofollow">http:&#x2F;&#x2F;www.acsu.buffalo.edu&#x2F;~keechung&#x2F;MGF743&#x2F;Readings&#x2F;G2%20D...</a><p>Since then, we have additional data points from the decimalized US equity markets. See <a href="http:&#x2F;&#x2F;www.sec.gov&#x2F;rules&#x2F;other&#x2F;2014&#x2F;34-72460.pdf" rel="nofollow">http:&#x2F;&#x2F;www.sec.gov&#x2F;rules&#x2F;other&#x2F;2014&#x2F;34-72460.pdf</a> for a bibliography. The weight of the evidence points towards thinner books. Incidentally, the SEC is looking to increase the tick size for illiquid small-cap stocks for this very reason.