Is it a blip or trend? The question arose as soon as the Census Bureau released data showing a drop in labor-force participation by mothers of kids under age 1. The study says 55 percent were in the workforce last year, versus 59 percent in 1998—the first real decline since 1976, when the rate was 31 percent. The drop was concentrated among white, college-educated, married women over 30. In its coverage of the data, The New York Times quoted experts who speculated that the then-robust economy made mothers comfortable about leaving work—suggesting the decline was a blip. But one could argue that the opportunity costs of leaving white-collar work were higher in the boom years of 1998-2000 than at any time in history—a factor that would tend to keep people in the labor force unless they were determined (for non-economic reasons) to quit. Thus, maybe it is a trend.