by Calculated Risk on 5/01/2009 03:00:00 PM

Here is a common question:

Q: I was looking at the Q1 Advance GDP report, and it showed that PCE was up 2.2%. However the March Personal Income and Outlay report showed that real March PCE was off -0.2%, after increasing 0.1% in February, and 0.9% in January. How did they get 2.2% for Q1 PCE growth? How does that compare to the monthly numbers?

A: First, the reported change in the Personal Income report is from the previous month (not annualized). The quarterly GDP report is the annualized change from Q4 to Q1.

Second, the quarterly change is from the average PCE in Q4 to the average PCE in Q1. Look at the following chart ...


Click on graph for larger image in new window.

Note: graph doesn't start at zero to show the change. All numbers are in billions.

This shows both the quarterly (red) and monthly (blue) PCE data (2000 dollars).

If you average October, November and December PCE, you get the Q4 PCE. And Q1 PCE is the average of January, February and March.

The math is simple: $8,214.2 (Q1 2009) divided by $8170.5 (Q4 2008) equals 1.00535. Take that to the 4th power (to annualize), subtract 1, and that gives the annualized rate of change in real PCE from Q4 to Q1: 2.2%.

Notice that the month-to-month change isn't useful in comparing to the quarterly change. Also notice that I didn't even report the March PCE numbers - that was mostly captured in the Q1 GDP report - and the monthly series is noisy.

The first two Personal Income reports each quarter are much more useful than the final month. When the April Personal Income report is released, the media will focus on the month-to-month change. However I will compare April PCE to January PCE - and then May PCE to February. This is the "two month" estimate for Q2 PCE (notice the calculation compares to the same month of the previous quarter, not the previous month).

For some time I had been forecasting a slump in consumer spending, and then using the two month method, I was able to declare the slump had arrived, see: Personal Income for August Indicates Consumer Recession and Estimating PCE Growth for Q3 2008

[T]his will be the first decline in PCE since Q4 1991. This is strong evidence that the indefatigable U.S. consumer is finally throwing in the towel.

I was also among the first to point out PCE would probably be positive in Q1: February PCE and Personal Saving Rate

This suggests that PCE will make a positive contribution to GDP in Q1.

The monthly data is extremely useful for forecasting - especially the first two months of each quarter.