المصدر: http://www.bls.gov/cps/cpsaat4.pdf؛ وhttp://www.bls.gov/cps/cpsaat3.pdf؛ وhttp://www.bls.gov/cps/cpsaat2.pdf.
资料来源：http://www.bls.gov/cps/cpsaat4.pdf；http://www.bls.gov/cps/cpsaat3.pdf和http://www. bls.gov/cps/cpsaat2.pdf。