Over the weekend, the Journal reported on the economics of “right-to-work” rules. The conclusion: It’s complicated, especially when it comes to proving cause and effect. But at a very basic level, right-to-work states have lower unemployment rates and faster job growth, but also lower wages.

A number of readers, however, noted that looking only at hourly or weekly wages fails to account fully for unions’ impact on their members’ paychecks. Dues eat into higher wages, while better benefits provided under union contracts don’t show up in wage data. Quantifying such impacts is difficult, but government data allow for a rough approximation.