flat lay photography of vegetable salad on plate

Correlation? Causation? YOU decide! (It’s as good an approach as any…)


So, I’ve concluded that we might as well give up on trying to spread the word about the correlation-causation fallacy. People just don’t seem to be getting it. I do appreciate that there are complexities (after all, causality causes, and is therefore correlated with, correlation, but correlation does not cause causality) but at the same time, some cases are pretty straightforward.

I mean, imagine you read about some research showing that people who score high for optimism also eat lots of vegetables. There’s a correlation right there. To flesh things out a little, imagine you read this specific study — ‘Association Between Optimism and Serum Antioxidants in the Midlife in the United States Study’ — recently published in the leading academic journal Psychosomatic Medicine.

You will find that the researchers do not know whether these people were optimistic throughout their lives or whether they were longstanding vegetable fans. All they know is that people who are optimists now tend to like a bit of carrot. I wonder what could possibly be going on?

Hmmmm. Optimism makes you think positively about your future, right? Well, maybe optimistic people look after their health because they wish to extend their lives in order to enjoy all the wonderful experiences they are optimistically looking forward to. Seems straightforward to me.

I suppose we would have to allow for the alternative possibility — that eating cabbage changes your brain and makes you predict future positive events — given that the study is, after all, cross-sectional. So, at best we can say that the study is inconclusive.

But not if you’re the Daily Mail it seems:

Another good reason to eat your greens: It makes you more optimistic about the future. 

People who eat plenty of fruit and vegetables tend to be more optimistic about the future, new research suggests…One theory is that antioxidants [found in fruit and vegetables] might have a de-stressing effect…[The researchers] found that people who ate two or fewer servings of fruits and vegetables a day were significantly less optimistic than people who ate three or more servings a day…

While the article does suggest that things might be vague, and alludes to the fact that the study attempted to control for extraneous variables (such as exercise and smoking), it does not explicitly point out that the study was cross-sectional. Or therefore, that conclusions about causality could go either way. Or, that further evidence on the temporal emergence of, on the one hand, diet, and on the other, optimism, would be needed in order to begin sorting the whole thing out.

Anyway, I’ve decided that the correlation-causation fallacy is too difficult. Therefore, I’m figuring that from now on causality should be determined by popular vote. So let X = “being an optimist“, let Y = “eating lots of fruit and veg“, and now GET VOTING

Feel free to base your response on your philosophical approach to vegetables, your belief in the right of government to tell us what to eat, your favourite vegetable, something somebody said to you the other day, your perception of the way foreigners seem overly fond of vegetables, your favourite optimist, or quantum entanglement…

Let’s settle this once and for all. I’m hungry.

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