Real GDP reached its low point in the second quarter of 2009, while the value of real GDI was essentially identical in the second and third quarters of 2009.The average of real GDP and real GDI reached its low point in the second quarter of 2009.
There were two reasons for selecting the earlier date.
The first was described above -- the fact that quarterly real GDP and GDI rose strongly in the fourth quarter.
The committee concluded that strong growth in both real GDP and real GDI in the fourth quarter of 2009 ruled out the possibility that the trough occurred later than the third quarter.
The committee designated June as the month of the trough based on several monthly indicators.
The second was that real GDI is a more comprehensive measure of income than real personal income less transfers, as it includes additional sources of income such as undistributed corporate profits.
The committee's use of income-side measures, notably real GDI, is based on the accounting principle that the value of output equals the sum of the incomes that arise from producing the output.Apart from a random statistical discrepancy, real GDI satisfies that equality while real personal income does not.The committee also maintains a quarterly chronology of business cycle peak and trough dates.The trough marks the end of the declining phase and the start of the rising phase of the business cycle.Economic activity is typically below normal in the early stages of an expansion, and it sometimes remains so well into the expansion.In particular, in 2001-03, the trough in payroll employment occurred 21 months after the NBER trough date.