In addition, the output gap may have been underestimated during this period. The existence of such a mistake has been given an important role during the period by many analysts. Such a consistent string of mistakes would not be too surprising. During this period, productivity and potential output both exhibited a surprising slowdown in growth, a development which is still largely unexplained by economists. At the same time, demographic factors, especially the entrance of the baby boom generation into the labor force, created an increase in the natural rate of unemployment that also was unexpected. Indeed, there was a widespread view that an unemployment rate of 4% was a suitable benchmark rate for policy. In contrast, recent (time-varying) estimates of the natural rate that prevailed during this period are in the 6 to 6½% range (e.g., Gordon 1997). Both of these factors–an underestimate of the GDP gap and the natural rate of unemployment–could have contributed to unduly easy policy, since it may have appeared at the time that inflationary pressures were less severe than they really were.