That's not how I interpret the data and that's not how Levitt interpreted the data. There was a dramatic increase in incarceration during the late eighties and into the nineties. In fact, this was the reason he identified as the single most important for the decline in violent crime in the 1990s. This was based on his work in a series of articles he has published.
On November 27th, 2006. See this statement in context.