A number of studies have pointed to the potential benefits of workplace wellness programs – from increased gym use to decreased health care spending. But what wasn’t clear was whether wellness programs are really making people healthier, or whether healthier people are more likely to enroll in them. A new study suggests it’s the latter.
The study, which involved close to 5,000 volunteers working for the University of Illinois Urbana-Champaign, was not an observational study, but what’s known as a randomized controlled trial. That means people were randomly divided in two groups, and one group was offered a workplace wellness program and one was not. When the researchers compared the two randomly divided groups, they found no difference in gym attendance, health care spending or other benefits that had been attributed to these programs.
Physician-writer Aaron Carroll explained in his New York Times column that because previous studies were observational studies, they can introduce selection bias. When the authors of the new study examined their data as if it had been an observational study, they saw that only about half the people in the intervention group opted in, and when those were compared to the ones who had the opportunity but didn’t take it, the data showed clear differences in gym visits, health care and hospital spending. But it’s unlikely the wellness program was the cause.
This doesn’t mean people shouldn’t do observational studies, or that the public should ignore them, said Alan Brookhart, a professor of epidemiology at the University of North Carolina Chapel Hill. A few years ago, he and a pair of colleagues wrote a primer for physicians on interpreting observational studies.
In the primer, he and the other researchers argued that this same kind of bias led the medical community to wrongly assume that hormone-replacement therapy prevented heart disease in post-menopausal women. Doctors began prescribing hormones to women as a routine preventive measure. Randomized controlled trials later showed no cardiovascular benefit and a range of previously unidentified harms.
On the other end of the spectrum, people who are very sick are less likely to partake of preventive health measures, and it can then look like their opting out caused them to die, when it was the fact that they were dying that caused them to opt out.
Brookhart said this explains some otherwise unlikely data showing that in an elderly population, people who got flu shots were 50 percent less likely to die than those who didn’t. This included deaths from all causes – not just flu. How could a flu vaccine have such an effect on nonflu deaths? To investigate, he said, he and his colleagues looked at the same correlation before flu season started. It was still 50 percent, but at that point there would have been very few cases of flu. The correlation was more likely caused by the fact that people who were near death, for a host of reasons, were much less likely to get a flu vaccine.
William Shrank, lead author on the observational-studies primer and now chief medical officer for the University of Pittsburgh Medical Center insurance service, agreed that observational studies can be a great tool for medical research. But people using the studies have to be mindful of cause and effect.
And despite the negative implications of this newest study, workplace wellness programs may still benefit employees. It may be that the health conscious would still go to the gym, or yoga class, and would still get their flu shots and have their blood- pressure checked, but they may still appreciate employers making it easier for them.
Faye Flam is a Bloomberg Opinion columnist.
