Two years later, President Jimmy Carter set up yet another panel to examine the unemployment statistics, with George Washington University economist Sar Levitan at the helm. I’m not clear on what led Carter to do this (people at the BLS seemed to think it was a waste of time), but one of the Levitan Commission’s main findings was that the classification of discouraged workers was still too arbitrary, and that people should be counted as discouraged only if they had looked for a job sometime in the past six months. (Remember, only people who have looked for work in the past four weeks are counted as unemployed.)

It took a while, but the BLS and Census Bureau finally adopted a weakened version of this recommendation in 1994, from then on counting only people who had looked for work in the past year as discouraged (with those who last looked more than a year ago counted simply as out of the labor force). In test surveys conducted in 1993, the change was found to reduce the reported number of discouraged workers from 1.1 million to just 424,000. This had no impact on the headline unemployment rate, because discouraged workers had been excluded from that calculation since 1945, but it did affect some of the alternative unemployment rates that were rejiggered in 1994 as U-1 through U-6.

Other changes made in 1994, which the BLS and Census Bureau said were occasioned partly by the growth of services and the entry of women into the workforce and partly by the availability of laptop computers for survey takers, had the effect of raising the headline unemployment rate by half a percentage point during the test year of 1993. The main reason was that changes in the wording of questions -- especially the switch from “Did you do any work at all last week, not counting work around the house?” to “Last week, did you do any work for pay?” -- led to more women being classified as both employed and unemployed.

Since 1994, there haven’t been any meaningful changes to the unemployment-survey questions. There have been lots of minor changes in methods, mainly to the population controls used in weighting the surveys, and there’s been a decline in survey response rates that could well be pushing the unemployment rate down slightly.

I don’t want to dismiss concerns that these changes, or the bigger shifts in 1994 and 1967, can make unemployment comparisons misleading—although, as I wrote Tuesday, I would dismiss the charge that the Obama administration or its predecessors have been actively manipulating the unemployment rate.