19All the authors cited above used U.S. data. Nielsen and Vissing-Jorgensen (2006) used Danish data and estimated σ2 = 0.005
 ψ  and σ2 = 0.015
 ξ  . It would be reasonable to interpret their estimates as the lower bounds for the U.S., given that their administrative data is well-measured and but that Danish welfare is more generous than the U.S. system.