Sonnemans, J. (2006). Price clustering and natural resistance points in the Dutch stock market: A natural experiment European Economic Review, 50(8):1937--1950.

This paper focuses on the tendency of stock prices to cluster at round numbers (like 10, 20, 30, etc. and to a lesser extent 5, 15, 25, etc.) and the related effect of round number price barriers (prices pass round numbers less frequently than other numbers). Two competing hypotheses are tested, using data from the Dutch stock market of the period 1990-2001. After 1 January 1999 stock prices were listed in euros, while guilders were still the currency of daily life until 2002. The aspiration level hypothesis predicts that round number effects in guilders will only slowly disappear. The odd price hypothesis predicts an abrupt change in round number effects after 1 January 1999. Generally, the results are consistent with the odd price hypothesis.