Whoís putting in long hours?

[T]here has been a reversal in the relationship between wages and hours. In 1983, the most poorly paid 20 percent of workers were more likely to put in long work hours than the top paid 20 percent. By 2002, the best-paid 20 percent were twice as likely to work long hours as the bottom 20 percent. In other words, the prosperous are more likely to be at work more than those earning little. This trend has been a puzzle for some economists.