Coffee and correlation

In the recent few weeks, there have been some studies with good news about coffee and a long life. See NY Post and Harvard. In both cases, there seems to be a relationship between coffee and long life. It did not seem to matter if the coffee drinkers preferred caffeinated or decaffeinated coffee or the sweetener they used.

The problem with these studies is that they do the research process backward. They find a relationship and try to explain it. The correlation is a relationship between two variables. Correlations do not mean causation. When someone starts with a correlation and looks for a cause, it makes for some faulty reasoning.

It is easy to conclude that coffee leads to longer life, in part, because that is what we want. We would prefer to make our lives better with things we love — coffee, chocolate, wine, and puppies. While it is still possible that there is a positive effect of these enjoyable products, the studies are far from being able to show the positive effect.

There could be many causes. For example, the person that drinks several cups of coffee a day can afford several cups of coffee (time and money). As a result, it is likely that such a person is different from the population as a whole. The reader of this blog may be thinking, “I drink several cups of coffee and I am not rich.” That is also a false assumption. If you can read these words you are literate, have time to read, and the money to buy communication equipment. The reader thus described is also unusual.

The actual researchers do not promote these conclusions. The problem comes in the way media reports the results. In a competitive media environment, the media and the public want the latest news. Speed is valued more than accuracy. We can get an updated report tomorrow. The problem is that research operates at a different pace. The updated information will not come tomorrow. It will come years down the road after we have all increased our coffee consumption in hopes of a longer life.

The public needs a more finely tuned suspicion of “research” evidence. Suspicious people like to say they “do their own research.” The result is that they usually find multiple copies of the same misguided conclusion. Instead, it would be far more effective to actually read the research reports for clues. For example, the two studies cited above came from Briton and Southern China — two areas not known for heavy coffee drinking.

The reader should consider why the research was done. What led the researcher to look at this association. Valid research does not occur in a vacuum. Earlier studies led the researchers to test (or retest) a particular relationship. The question of why this effect is believed to occur is more important than the findings. Without a reason, it is far more likely to be incomplete research looking for a media payday.

Let the reader beware.

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