In the past 40 years, regular working Americans have barely seen their salaries grow, while around them, the cost of housing and basic needs have skyrocketed, as has pay for business executives. What’s behind this decline? Economists and political scientists often point to the decline of labor unions in those same years as a major contributing factor to the current environment of soaring business profits and meager worker salaries.

When unions were at their strongest before the 1960s, they helped narrow the gulf between worker and executive pay (which currently stands at 312 to 1), and lobbied for higher minimum wages and better access to health care. Researchers have also speculated that unions created positive spillover effects at nonunionized workplaces, where managers may have introduced higher salaries and better benefits in an effort to head off organizing efforts among workers.

Findings like these, however, tend to rely on cross-sectional population snapshots, rather than assessments of individuals over time. In other words: There was not sufficient evidence to prove that unions substantially improved individual people’s outcomes over the course of their careers. Absent that evidence, it became almost too easy to blame people’s current economic struggles on their failure to work hard enough, or pull themselves up by their bootstraps.

But in a new study, University of Illinois sociology professor Tom VanHeuvelen finds that unions created benefits for individual workers, and that their decline is directly responsible for the lack of cash in workers’ bank accounts.

“Unions are important for establishing and amplifying norms and values of egalitarianism; unions provide a dialogue about things like worker rights; unions fight for social policies that are broadly beneficial to everyday workers and normal people,” VanHeuvelen says. These are all macro benefits that have unraveled as unions have declined; that much is indisputable. But what VanHeuvelen wanted to find out was to what extent these benefits affected individual outcomes, and in his paper, he found what he calls “remarkably robust” evidence that the presence of unions created benefits over the course of an individual’s career, and conversely, the absence of unions creates barriers to success on a highly personal level.

To arrive at this conclusion, VanHeuvelen pulled data from the Panel Study of Income Dynamics, longitudinal study of over 18,000 individuals in over 5,000 families that began in 1968, which is currently the longest-running household panel survey. By working with data from individuals over time, VanHeuvelen was able to account for demographic factors like educational attainment, race, gender, geographic location, and industry-switching, which some economists argue have more bearing than the presence of unions.

“Typically, you hear people say that these benefits like higher wages are not the result of unions–it’s people’s inherent abilities or demographics, and if you could measure for those, you would find that union effects are smaller, or not there at all,” VanHeuvelen says. That assumption, he says, did not play out in his research.