Earlier this week I was part of an email chain where it was discovered that with the new 2008 ACS data which was just release there was a national change in workers from 2007 of about 4.8 million for a growth of about 3.4 percent. Of course this seemed odd given the year that we have been through. I further learned that BLS was showing a loss of workers during the same time which prompted me to pass the issue over to Melissa Chiu our CTPP coordinator at the Census Bureau. Here is what Melissa had to say. Hi Ed, I spoke with the subject matter branch chief and it turns out that the Bureau recommends using caution when making labor force comparisons between data from 2008 or later and data from prior years (make sure to look at the footnote at the bottom of the labor force tables). This is because there was a question change starting in 2008 that results in more people responding that they worked last week. The question in use before 2008 missed many marginal workers. Essentially the data are better now and this also puts the ACS data more in line with the Current Population Survey (CPS)-based BLS data. In addition, as far as labor force estimates go, the BLS data are considered the official estimates, and many more questions are asked on the CPS regarding employment than on the ACS. So there may still be differences between CPS and ACS due to this and other issues. There is more information on this question change in the research note: http://www.census.gov/hhes/www/laborfor/researchnote092209.html The note references the following 2006 content test report that resulted in the question change: http://www.census.gov/acs/www/AdvMeth/content_test/P6a_Employment_Status.pdf Finally, for other information on labor force data, please start here: http://www.census.gov/hhes/www/laborfor/laborforce.html I hope this helps. If you have further questions, please let me know and I will refer you to the appropriate person. Thanks, Melissa -- Ed Christopher 708-283-3534 (V) 708-574-8131 (cell) FHWA RC-TST-PLN 4749 Lincoln Mall Drive, Suite 600 Matteson, IL 60443