Why Isn't Ohio's Indoor Smoking Ban Reducing Smoking?

In 2006, Ohio voters approved a ban on smoking indoors, including bars and restaurants. The ban took effects in December 2006. One would think that the prohibition would reduce smoking rates, right? After all, the prohibition increases the costs of smoking quite significantly for many smokers (particularly in the winter). Yet according to this story, the smoking rate in Ohio has increased by three percent since 2007. What gives?