Correlation, causation, and association – What does it all mean???
June 4, 2009 – 8:44 amWelcome to All About Addiction, THE online source for addiction education and tips. If you're like most of our new readers, you're lost and looking for help - our categories on the left and search bar on the right, will help you find what you're looking for.
To stay updated, you may want to subscribe to my RSS feed or Newsletter.
We're always looking for stories from readers - And don't forget to give us a Stumble or a Digg!
By the way: If you go to the actual post page by pressing on its title, you'll get a list of related posts as a bonus! Enjoy.
A comment posted by a reader on a recent post reprimanded me for suggesting that marijuana caused relationships to go bad.
In this instance the reader was mistaken, as I had specifically used the word “associated”, but the comment made me think that maybe I should explain the differences between correlation, causation, and association. I’m a scientist studying addiction, and in the field, it’s very important to be clear about what each of the words you use means.
So let’s get into it:
Correlation - When researchers find a correlation, which can also be called an association, what they are saying is that they found a relationship between two, or more, variables. For instance, in the case of the marijuana post, the researchers found an association between using marijuana as a teen, and having more troublesome relationships in mid, to late, twenties.
Correlations can be positive – so that as one variable (marijuana smoking) goes up, so does the other (relationship trouble); or they can be negative, which would mean that as one variable goes up (marijuana smoking) another goes down (grade point average).
The trouble is that, unless they are properly controlled for, there could be other variables affecting this relationship that the researchers don’t know about. For instance, education, gender, and mental health issues could be behind the marijuana-relationship association (these variables were all controlled for by the researchers in that study).
Causation - When an article says that causation was found, this means that the researchers found that changes in one variable they measured directly caused changes in the other. An example would be research showing that jumping of a cliff directly causes great physical damage.
Most of the research you read about indicates a correlation between variables, not causation. You can find the key words by carefully reading. If the article says something like “men were found to have,” or “women were more likely to,” they’re talking about associations, not causation.
Why the difference?
The reason is that in order to actually be able to claim causation, the researchers have to split the participants into different groups, and assign them the behavior they want to study (like taking a new drug), while the rest don’t. This is in fact what happens in clinical trials of medication because the FDA requires proof that the medication actually makes people better. Obviously, it is much more difficult to prove causation than it is to prove an association.
So should we ignore correlations?
No! Correlations are still important and still need to be looked at, especially in some areas of research like addiction.
We can’t randomly give people drugs like methamphetamine as children and study their brain development to see how the stuff affects them, that would be unethical. So what we’re left with is a need to study what meth use (and use of other drugs) is associated with. It’s for this reason that researchers use special statistical methods to assess associations, making certain that they are also considering other things that may be interfering with their results.
In the case of the marijuana article, the researchers ruled out a number of other interfering variables known to affect relationships, like aggression, gender, education, closeness with other family members, etc. By doing so, they did their best to assure that the association found between marijuana and relationship status was real. As more researchers assess this relationship in different ways, we’ll learn more about its true nature.
This is how we found out that smoking causes cancer. Through endlessly repeated findings showing an association. That turned out pretty well, I think…
Sphere: Related Content
Related posts about addiction
Tags: addiction, association, cancer, causation, correlation, FDA, marijuana, medication, meth, relationships, research, smoking, statistics
Loading ...