“It’s official: Dog owners live longer, healthier lives” reads the headline on Time’s website. The refreshing change is that the headline – and the article – carefully explain that the data are correlational, not causal (MacMillan, 2017). When this article appeared in my local paper, The Seattle Times, it came with a sub-headline: “It may be correlation, not causation, but the risk of death was about 33 percent lower for dog-owners than non-owners, a study found.” You won’t be surprised to hear that the journalist, Amanda MacMillan, has a BA in journalism/science writing with minors in “science, technology, and society” and physics [shout out to Lehigh University, her alma mater.]
Researchers looked at national records for 3.4 million people in Sweden over a 12-year span. Those records included whether the people registered a dog and their health reports. “Dog ownership registries are mandatory in Sweden, and every visit to a hospital is recorded in a national database.”
Researchers learned that “[p]eople who lived alone with a dog had a 33% reduced risk of death [over that 12-year span], and an 11% reduced risk of cardiovascular disease, than people who lived alone without a dog.” The findings were less pronounced for people who lived with other people,
I’m going to put this study into my correlation lecture. After sharing these results, I’ll ask students to work in pairs to generate possible reasons for these relationships and then share their ideas with the class. This is a nice opportunity to show that while correlations do not tell us about cause and effect, they provide a goldmine of hypotheses for future research.
One possibility, the article points out, is that owning a dog causes better health in the owner: owning a dog causes people to be more active (“gotta walk the dog”). Or dogs may share their microbiome with their owners, giving their human immune systems a boost – as I reflect on how I woke this morning with my dachshund standing on my head and licking my face. Or by walking our dogs, we meet people, extending our social network; social networks are also correlated with better health.
Another possibility, the article also points out, is that more active (read “healthy) people are more likely to get a dog.
And then there are the third variables. For example, “[o]ther studies have suggested that growing up with a dog in the house can decrease allergies and asthma in children.” It may be that having a dog growing up made people more likely to get a dog as an adult and that the exposure to dogs as children gave us a stronger adult immune system.
As instructors of psychological science, let’s continue to help our students understand what research does and does not tell us, so that when they get jobs as journalists, they can accurately interpret research findings for the general public as this journalist has done.
MacMillan, A. (2017, November). It’s official: Dog owners live longer, healthier lives. Retrieved from http://time.com/5028171/health-benefits-owning-dog/