Post Hoc, Ergo Propter Hoc?!?

One of the few things I remember clearly from my seventh grade year at Harvey Lewis Junior High School was taking Social Studies class. Mrs. Hancock, a portly but not unattractive woman, was the teacher. The Vietnam War was gaining momentum, and it seemed appropriate to Mrs. Hancock to teach us how to wade through all of the media coverage of the war, and to help us to understand how that coverage can actually create our perspective. Her first lesson was on the various propaganda tools currently employed by the media to—as she saw it—promote the war to the American public in its rhetoric. We were introduced to such terms as “glittering generalities,” “argument against the man,” and “red herring,” among others.

The one that stuck with me over the years was what was called the post hoc, ergo propter hoc fallacy, which is Latin for: after this, therefore because of this. It has stuck with me so tenaciously, I think, because we so often use this fallacious reasoning to explain a lot of what occurs in our daily lives. For example, if we wash and wax the car and then it rains, our resultant thinking is that it was the act of washing and waxing the car that caused the rain: it rained after the wax job, therefore, it rained because of the wax job.

It’s a natural tendency of humans to employ post hoc, ergo propter hoc reasoning. And it’s even a little funny when we realize just how ridiculous the idea is that, because one particular event follows another-which is to say, the two events are closely associated, or corrolated- the one event must have caused the second event. Washing the car caused the rain. Yeah, right. Ha ha.

And yet, funny as it might seem, some of us actually believe the “corrolation means causation” fallacy. My wife, Jeanie, who was at one time a practicing doula (a birth and post-partum coach for mothers) tells me of some of the strange beliefs pregnant women have had throughout history: eating strawberries will give your kids a birthmark; if your back gets cold, your milk will dry up. And who hasn’t heard this one from his or her parent: you cross your eyes like that and they’ll get stuck that way? We listen to these and laugh.

But it’s not so funny when the scientific community, whose practitioners should know better, and the media who report on that community’s research studies, fall into the post hoc, ergo propter hoc trap. Unfortunately, and often incredibly, it happens all the time. What makes their falling into this trap such a travesty is that the American public holds its scientists and its media in such high esteem. We believe what they have to say, on just about anything-and in particular, about what is and what is not healthy for us. And we will alter our lifestyles according to their pronouncements, with sometimes disastrous results.

I mention this because of an article I ran into just this morning on MSN.com entitled “Surprising Signs You’ll Live Longer Than You Think.” The article listed thirteen “signs” that you’re likely to live longer if you tend toward meeting certain “science-based” criteria. Here are those alleged signs, together with why, briefly, the scientists believe them to be true:

  • Your mother had you young (her ovum were healthier at a younger age)
  • You’re a tea lover (tea contains substances beneficial to the heart)
  • You’d rather walk (“fit” people live longer)
  • You skip soda-even diet (sodas contain substances known to be harmful)
  • You have strong legs (lower-body strength decreases your likelihood of falling and injuring yourself as you age)
  • You eat purple food (grapes, blueberries, etc. contain substances that aid the heart and help ward off Alzheimer’s Disease)
  • You were a healthy-weight teen (being overweight as a teenager has been linked to developing Diabetes as an adult)
  • You don’t like burgers (red meat and processed meats have been linked to the development of colorectal cancer and other cancers)
  • You’ve been a college freshman (folks who went to college are statistically less likely to begin smoking)
  • You really like your friends… (good interpersonal relationships help ward off stress)
  • …and they’re healthy (having fat friends increases your own likelihood of gaining weight)
  • You don’t have a housekeeper (doing your own housework is a great way to burn calories)
  • You’re a flourisher, not a languisher (flourishers are optimistic and derive meaning from their lives, both of which lead to behaviors likely to increase longevity)

Of course, I was amused by the article. My first response was to see where I fit within the schematic laid out in the list. I have always had strong legs; my mother gave birth to me when she was nineteen; I love tea. Hmmm. So far, so good. Then I got to the item that says “You don’t like burgers.” Immediately something seemed to grab me in the stomach and twist: I’ve always loved burgers. Then I read this in the explanation:

“A few palm-size servings (about 2 1/2 ounces) of beef, pork, or lamb now and then is no big deal, but eating more than 18 ounces of red meat per week ups your risk of colorectal cancer-the third most common type, according to a major report by the American Institute for Cancer Research. Colorectal cancer risk also rises by 42 percent with every 3 1/2-ounce serving of processed meat (such as hot dogs, bacon, and deli meats) eaten per day, the report determined. Experts aren’t sure why red and processed meats are so harmful, but one of their suspects is the carcinogens that can form when meat is grilled, smoked, or cured-or when preservatives, such as nitrates, are added. ‘You can have an occasional hot dog at a baseball game, but just don’t make it a habit,’ says Karen Collins, R.D., a nutrition advisor at AICR.”

More twisting in my gut: I love hot dogs, and kielbasa, and corned beef. Jesus, I thought, was I at risk for cancer? Did this mean I had to make a radical change in my dietary habits, or else?

Then I remembered Mrs. Hancock and my seventh-grade social studies class, and the old post hoc, ergo propter hoc fallacy. I wasn’t entirely certain that that was what I was witnessing here, but I thought I’d do a little research into the subject to find out. Here’s what I discovered:

The most recent research into the link between red meat/processed meat and the development of colorectal cancer was conducted less than a year ago, and was reported in the Journal of the American Medical Association. This study has been fodder for a slew of articles citing causality between the consumption of red meat/processed meat and the development of cancer. Here’s a link to the actual abstract of the study. It is the Conclusions section that is the most interesting. It reads:

Higher intake of a Western dietary pattern may be associated with a higher risk of recurrence and mortality among patients with stage III colon cancer treated with surgery and adjuvant chemotherapy. Further studies are needed to delineate which components of such a diet show the strongest association.

Key words to pay attention to: “…may be associated” and, “strongest association.”

Ah. I was glad to have read it. I breathed easier and resurrected my wife’s and my meal plan for the week, which calls for bacon, steak, corned beef, and kielbasa, and generous amounts of animal fats. I’m not a scientist. But I have been around the block enough to know this: any researcher worth his salt (which, by the way, has been shown to not raise blood pressure, as previous scientific studies indicated) will tell you that an “association” (indicated by observational studies and epidemiological evidence) proves exactly nothing. It’s a flag, nothing more, pointing to a relationship which hasn’t even begun to be defined, and to the need for further inquiry via studies rigorously adhering to the tenets of the scientific method.

The problem, as I see it, is this: the scientists in the aforementioned study never claimed to have proven a causal link between eating red meat/processed meat and developing colorectal cancer. They merely cited an association. Unfortunately, the media don’t seem to understand what “association” means. They hear “association” and report “cause.” And we, the reading public, who hold our media in such high esteem, believe their reportage. And why wouldn’t we? We have to trust someone, don’t we? Aren’t the media supposed to know better? Don’t they check their facts?

Indeed. I have ideas about that which I might explore in a later post. But for now, I think it’s prudent to remember the few odd lessons we encounter during our lives which, if we pay attention to them, can help us to navigate through the morass of conflicting information we’re bombarded with, even from sources we believe to be authoritative. For myself, I’m thanking Mrs. Hancock who, forty-four years ago, taught me to “believe only half of what you see, and nothing that you hear (read),” and–most important–to “question authority.”

It’s probably the best lesson I ever learned.

Leave a Reply