The August issue of of the Journal of Criminal Justice has an interesting article on the use of supermax in Florida.  From the article: Supermax Housing: Placement, Duration, and Time to Reentry:

[T]he study found that supermax inmates typically experienced multiple placements in supermax housing. For example, 55 percent of supermax inmates experienced three or more episodes of supermax confinement. The study also found that, some inmates spent but a few months, or a small percentage, of their total prison term in such housing, while others spent much more time in it. To illustrate, for 44 percent of all supermax inmates, supermax confinement constituted less than 15 percent of their total term of incarceration; even so, for 14 percent of supermax inmates, supermax confinement constituted over half of their total term of incarceration. The analyses also revealed that 28 percent of inmates were released from supermax housing within three months of their return to society and 44 percent were released from it within six months of their return.

Logistic regression showed that violent behavior was the strongest predictor of supermax confinement: