The same is true of pet ownership. People who are given cats know that they have been given cats. There are no placebo cats. So there are studies that compare people in the real world who have lived with and without pets. This is the more feasible and accurate approach to understanding the effects of pets on human health. But the constant and gnawing limitation is that it’s difficult—if not impossible—to prove what sorts of behaviors are actually causing better or worse health outcomes. It took decades just to confirm that smoking was actually causing the mid-20th-century surge in lung cancer.
So what Parast did was look at all the variables that come with owning a pet—like living in a larger home and having greater household income. To be a confounding variable, a factor has to be associated with both the likelihood of owning a pet and with the outcome—in this case, child’s health (mental or physical).
After distilling all of these factors out of the equation, it turned out that the cats (and dogs) themselves were not associated with better health. Pet ownership is more of a signifier of the sort of life that leads to better health, not the driver of that better health. “We’re not completely ruling out that pet ownership leads to good health,” said Parast. “We’re just saying you need to step back and see that people who own pets are different from people who don’t in a whole lot of ways.”
The study can’t rule it out because it had a serious limitation. That’s what gives me hope, and Parast, too. It was a cross-sectional study, meaning it only studied people at a single point in time. (e.g., Does your house have a dog? Does your child have asthma?)
To really understand this relationship, a study would need to follow kids over time and see if they grew up healthier. This remains to be done on a large scale.
“I think there are many other positive benefits to owning a pet besides thinking that it will improve your health,” said Parast. “Obviously having a pet brings joy and companionship and a multitude of other things.”
I noted that those things are associated with mental health and physical health.
“Right,” she said. “But we don’t have measures of long-term outcomes to test that. I’ve heard people say that having a pet teaches responsibility, which is hard to measure. And if you really wanted to measure it, you’d test something like, 10 years later did this kid grow up to be someone who can hold a job?”
That sort of cohort study could also help understand how pet ownership may lead to better health. The idea is that, given this sort of longitudinal data over time, researchers could compare pet owners and non-owners, and then for example, five years later look at differences in physical activity among both groups. Then some years after that, researchers could look at health outcomes, and they could determine if maybe that physical activity is a mediating factor between pet ownership and health, meaning that essentially owning a dog does make people healthier.
“That would be great,” she said. “I mean, gosh, I hope that would find something. It would be great to have a reason to hand out cuddly puppies to everyone who needs better health. I would be completely in favor of that. But there’s no scientific evidence right now that shows that.”