Causation or Association
I love these discussions. What do scientific studies really tell us? It can be confusing and it can in some cases cause real issues for people with a chronic disease. This first came up for me with a modest visit to the dentist. I see the dentist 3 times a year for cleaning. It is an odd insurance deal but it works for me. He looked at my mouth after the cleaning, his general checkup, and he said an odd thing. He peered in my mouth and recommended that I get my teeth cleaned 4 -5 times per year, he has two hygienists to keep busy, so he always suggests cleanings at least 4 times a year. When he did this he offered a warning that gum disease causes Rheumatoid Arthritis (RA). I didn’t think much of it at the time and went about my business. Well two years later I was diagnosed with RA (I think I had been experiencing issues for several years) and I thought back on the discussion I had with my dentist.
Did not getting my teeth cleaned 5 times a year really cause RA? I mean if so could getting them cleaned 12 times a year have prevented other ailments? Could such a massive cleaning effort have prevented RA? Could it have prevented Type 1 diabetes? Did I just find the cure for all autoimmune diseases? I mean imagine not getting my teeth cleaned being the reason I got RA or Diabetes? Maybe it was the measles? I got the measles 5 times as a kid maybe that caused all my ailments? How about camping, I used to get lots of mosquito bites when I was a kid. It was sort of freaky.
So flash forward 14 years and I start my doctorate program and we are talking about the type research we would be doing. One woman in the class says that she wants to prove teaching reading to first graders improves second grade reading scores. If so, and I have no doubt it does help, she may have discovered the secret to improving second grade reading scores. The professor halts the discussion and launches into his lesson about the difference between causation and association. He challenges the student to demonstrate her proof for the statement she had made. She reported that she knew that the students of the one first grade teacher in her school who did 90 minutes of reading every day in her school had students who scored better on second grade reading measures. Of course she was that teacher.
Well that is a powerful statement but of course our professor was not satisfied. He challenged her further. He asked, do these students have less recess time? How about more parent work with students at home? Do they get less math instruction? How about buying more books? Perhaps there was a selection process that allowed children’s parents to request her class? Maybe her classroom had more or less sun?
Well by the time it was over the student was second guessing her assertion because she realized that there may have been a thousand different factors that influenced student reading scores in 2nd grade. So while her 90 minutes of reading might be associated with better 2nd grade scores she could likely never say it is was the cause. It was a lesson well learned by a group of students who were studying to do dissertations later in the program.
On the flight back to Indiana I was thinking about the lesson and I recalled this interaction with the dentist and I starting pondering what he had said. So I started reading the research about the connection between RA and teeth and gum issues. Of course diabetics tend to have a higher incidence of gum disease (association not causation). So does gum disease cause RA?
Well of course the research is pretty clear that there is an association. RA patients have a higher incidence of gum disease. That part is fairly well documented. But causing RA? Not so much. Researchers have not actually linked gum disease as the cause of RA. What my trusty dentist had done was pollute the science of the day to make it say what he wanted. Obviously researchers did not have 2 hygienists to support. So they might be less likely to lay the blame on the cause of RA on gum issues.
That brings me to the point of this little note. Sometimes we confront medical providers and lay people who bend science to mean what it cannot really say. I caution readers to think about things far more than I thought about them when I was diagnosed with RA. It is not always about what causes things. Sometimes, including our blood sugar rises or falls are more associative than casuistic. Here is another example. I walk past a Cinnabon in the mall and of course it smells so good. Later my Blood sugar goes up 75 points. I might say well smelling that Cinnabon shop spiked my blood sugar. Well of course we really know it was the ice cream I was eating at the time, but suppose I incorrectly assign blame to that wonderful smell? I might read the mall directory and figure how to stay away from the Cinnabon shop so I will never smell that again. In reality, I took an association and wrongly made it causation.
Be careful of assigning causation to association. The scientific measure of causation is a strong statement. Causation is a tough hurdle to overcome. Of course if something is shown by repeated experiments to be the cause of an event well that is a strong statement. But it is also a rare event. Rare events almost never occur, but two associated events, that is an easy hurdle to overcome. My dentist influenced by his need to keep two hygienists busy, confused it. After all If my dentist can make the mistake so can a regular individual.