| November, 1992 | Robert Repetto, Roger C. Dower, Robin Jenkins, and Jacqueline Geoghegan |
| June, 1997 | Robert Repetto and Duncan Austin |
| September, 2003 | Gilbert E. Metcalf, Tufts University and NBER |
| October, 2004 | Friends of the Earth, Taxpayers for Common Sense, U.S. Public Interest Research Group, et al. |
| June, 2005 | Craig Hanson |
| June, 2005 | Steve Ellis, Vice President, Taxpayers for Common Sense |
| June, 2005 | Gilbert E. Metcalf, Department of Economics, Tufts University |
| June, 2005 | Craig Hanson |
| July, 2005 | William G. Gale |
| January, 2006 | Craig Hanson |