Business cycle dating committee wiki
The committee concluded that some of the depressed level of economic activity in September 2001 was the result of the exceptional events of September 11, and thus should not be considered in identifying the trough.
Rather, the committee determined only that the recession ended and a recovery began in that month.
Based on this information, the committee concluded that the economy reached a trough in November.
The NBER's practice has been that if economic activity is roughly flat at the end of a recession or expansion, the turning point is placed at the end of the flat period.
Two other indicators the committee focuses on-payroll employment and industrial production-remain well below their pre-recession peaks.
Indeed, the most recent data indicate that employment has not begun to recover at all.