Have you ever participated in a “workplace wellness program” or known somebody who tried one? Did you notice any difference? If not — and you wouldn’t be alone — a team of enterprising policy analysts in Illinois may have found an explanation. They ran a neat little experiment on employees of the University of Illinois at Urbana-Champaign and wrote up the results in a recent working paper for the National Bureau of Economic Research.

First, 12,459 benefits-eligible university employees were invited to complete a 15-minute online survey about health and wellness. Roughly 4,800 bothered to fill out the survey, at which point they were randomly divided into seven groups. Six of the groups were offered varying levels of incentives to participate in a new wellness program. “Those who successfully completed the entire program earned rewards ranging from $50 to $350,” the researchers noted, “with the amounts randomly assigned and communicated at the start of the program.” Members of the seventh group were told they might be contacted for future surveys and were otherwise left alone.

After the program had run its course, the researchers — Damon Jones, David Molitor and Julian Reif — compared the people who were offered the wellness program with the people who were left alone. Thirty-nine wellness-related outcomes were measured, from sick days to health-care spending. The researchers found no significant effect in 37 of the 39 outcomes.