The SEC study concluded that "most evidence shows that the pilot had a minor effect. The most intriguing results are in volatility. Some evidence that the tick test has a bigger effect in small stocks." (Question/observation: If the tick test has a bigger volatility effect on smaller stocks, and that is presumably because the smaller stocks cannot handle larger volume brought about by the relaxation in trading constraints, what does that then say about the volumes created by the short-sided sector ETFs and the resultant effects on the underlying stocks? This never would have been picked up in the study, because the study was concluded before these short-sided sector ETFs were rolled out.)
The authors of the study made a couple of other interesting empirical observations. First, they noted that depth of quotes decreased in the pilot stocks. They conjecture that this is because a short-seller without an uptick rule is a liquidity demander, and the uptick rule may force them into being a liquidity supplier. This is fascinating, because many short-sellers argue about the liquidity they bring to the market, yet the evidence was that short-sellers were perhaps liquidity takers without the uptick rule.
The other intriguing statement the SEC staffers made was the caveat that perhaps during the pilot program, short-sellers with manipulative intentions were on good behavior, knowing that their actions were under scrutiny (and if they fouled it up, they may lose their chance to do away with the uptick rule).