USA Today 8.9.07 reported that new Census Bureau demographic data show "Young people are moving out of cities for neighborhoods in the suburbs and beyond." The article continued, "The 20-34 year old populations declined in Atlanta, Chicago, Dallas, Miami, NYC, and Seattle, while their numbers grew rapidly in nearby counties where housing is cheaper."

Problem is, these "facts" are based on estimates -- and rather odd ones, at that.

Here's how Impresa Consulting economist Joe Cortright explained it to us:

"The county level estimates are just that: estimates. They are not based on actual data on the age-specific breakdown of county populations.

"The Census Bureau uses IRS data on migration (changes in the addresses reported on 1040 forms) to estimate the total number of people moving from county to county, and then uses state-level demographic factors (race, age, etc) to estimate the demography of each county.

"Growing counties are automatically assigned more people in each demographic group than declining counties. This is not affected by whether more or fewer people of any demographic group are moving to a particular county within a state."

Explaining its methodology, the Census Bureau says:

"Domestic migration is estimated at the county level by allocating state-level migration to the counties in that state. . . . The use of this approach means that for both in-migration and out-migration the shares allocated to each county in a state have the same age-sex distribution as the state-level migration."

Joe continues his explanation, "It is fair to say that populations are growing in those suburban counties (where housing is cheaper). But it's impossible to know whether this is because of 20 to 34 year-olds or some other group, based on the underlying data used in constructing these estimates.

Here's the link to the Census Bureau methodology:
http://www.census.gov/popest/topics/methodology/2006_st_char_meth.html

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