Medical researchers are somehow allowed to get away with statistical murder. It upsets me to read the article in Forbes titled "Pet Owners May Have Lower Risk For Heart Disease." (link)
This article takes the form of many other similar articles that purport to find an association between some risk factor and a common disease. Note they always use the weasel word "may". If you see this word, and immediately trash the article, you won't be any worse off than the people who read the article.
The weasel word will inevitably lead to "causation creep". There it is in sentence 3:
Dr. Glenn Levine, a professor at Baylor College of Medicine, along with his colleagues recommend that people have a dog or cat as a way to lower the risk of heart disease.
If the researchers only discovered an association, how is it that owning a dog or cat will lower your heart disease risk? If that were true, then the researchers have discovered a cause, not a correlation.
Such drivel will inevitably lead to "story time", which is a string of make-believe theories that have no support whatsoever in the empirical research. There it is in sentence 4:
[Having a dog/cat lowers heart disease risk] occurs by people becoming more physically active, which ultimately can lower blood pressure, cholesterol, as well as lead to lower levels of stress.
While there are some studies (most of it of excretable execrable quality) that report correlation between pet ownership and heart disease risk, you will not find studies that link all of those items listed above.This means none of those items are proven. They are just theories.
What confuses people is that the transitive relationship does not usually hold in statistics: if you have A -> B in one study, and B -> C in another study, you do not know if A -> B -> C holds. In fact, A > B and B > C may not mean A > C, even in the same study (this is due to sampling variability).
After all of that, the last few paragraphs of the article serve to invalidate all that went before. Too bad the majority may have stopped reading by that point. (I encourage you to stop reading at the word "may" in the title.)
Dr. Levine came back to say this: "it may be simply that the healthier people are the ones that have pets, not that having a pet actually leads to or causes a reduction in cardiovascular risk." Then why did he and his colleagues tell us that having dogs or cats is a way to lower heart disease risk?
The American Heart Association has a hand in spreading this misinformation. In this paper, they just list all kinds of studies without regard to their quality.
Also notice that they never said owning pets will prevent heart disease. Reducing heart disease risk is not the same as reducing heart disease. In fact, the only two studies of "survival in people without established cardiovascular disease" both reported no statistically significant relationships between dog owners and non dog owners. I wouldn't trust any of these studies unless you pull out the study and carefully examine who the subjects were; almost all of these are observational studies with no control groups (non-pet-owners is not a control group).
What's wrong with "story time"?
Go to this blog where they have a laundry list of statistics about pet owners. I can make up a story or two based on any of the following data:
- Families with children are much more likely to have pets than families without children
- The age group most likely to own a dog is 18-24 year olds at 58%.
- 78% of dog owners own their own home. 18% rent.
- Blacks seem to be less likely to own pets because they are more likely to live in densely populated urban areas with less room for pets.