For a more up-to-date estimation of the union wage premium, I used data from the U.S. Census Bureau’s Current Population Survey and employ a similar regression analysis as those used in the aforementioned studies. These regressions analyses allows a comparison of the wages of workers whose only difference in the government data is whether or not they belong to a union. The results suggest that union wage premium has continued to decline since 2002, and in 2014, the CPS data show it to be an average of just 10.2 percent, including both private and public sectors.

But that’s not the end of the story, however, because it turns out that there are methodological assumptions made by the Census Bureau that bias this figure downward. The reason for this bias, in short, is that the Census Bureau imputes the wages for some survey respondents without considering whether these workers are unionized. So, even if these workers are unionized, there wages are categorized as nonunion wages by the Census Bureau.

Fortunately, the records for the survey respondents with imputed wages can be removed from the dataset and a slightly more accurate estimate of the union wage premium can be obtained, although the finding is slightly less robust as it relies on a smaller survey dataset. When this adjustment is made, the CPS data show the union wage premium in 2014 to be 14.7 percent, on average, almost half of what many unions consider it to be. The 15-year average (2000-2014) was 13.2 percent, with a high of 14.9 percent in 2010 and a low of 11.6 percent in 2009.