The plot thickens. Or maybe it … thinnens. I don’t know. The point is that the folks at the San Diego Chamber of Commerce have gotten to the bottom of our recent mystery about why their population data differed so much from that of the Census Bureau. Yet their answer has only raised another question.

The Chamber’s Rachel Laing elaborates:

The mystery of the difference in the migration data on the Chamber’s Web site and the U.S. Census bureau appears to have been solved. Kelly Cunningham, who headed the ERB for years before leaving in early 2005, helped us sort all of this out.

To sum it up, the Chamber uses California Department of Finance data, because the state agency is assumed to have better ability to track and estimate the state’s population changes. They also release their estimates in a more timely fashion – months ahead of the Census Bureau. SANDAG also uses DoF data over the Census Bureau data in its planning.

The discrepancy between Census Bureau and DoF data since the 2000 census is well-known among California economist types, apparently, with the largest discrepancy being between the two agencies’ estimates of out-migration; the Census Bureau’s are much higher. There are also notable estimate discrepancies among all the statistics of population change – births, deaths, domestic and international migration.

… I realize that this doesn’t explain why there is such a vast discrepancy between the two agencies’ numbers, but I wouldn’t want to ruin a good day of reporting for you on your next hot story: the Battle of the Statisticians. Because apparently this is a matter of dispute between the federal and state agencies.

In short, the Chamber’s report reflects the Department of Finance data – but the DOF data is itself different from Census Bureau data I used in my original comparison. So what accounts for this latter discrepancy, well-known though it may be?

I will certainly try to find out. For now, though, two things are clear: that “thinnens” isn’t a real word, and that I’ve been pestering the wrong people.

RICH TOSCANO

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