While the labor force participation rate is 62.4% down from 65.7% when the recession ended, those workers won’t return. They’ve retired, are students, are disabled or care for a family member. Slack is the sum of discouraged, marginally attached and those working part-time because they can’t find full-time work. That number, corrected for growth, is 1 million above its long-term average. Given a labor force of 157 million, it’s tiny.