Correlation and Causation

One of the most widely spread words of advice for college educated individuals, especially in STEM fields, is "Correlation does not imply causation." It is simply astounding how much misinformation is spread because this rule is not followed. Sensationalized media like Buzzfeed, The Telegraph, or the plethora of Facebook clickbait sites will post articles titled "Eating Chocolate Makes You Smarter!" based on demonstrated correlations like the graph below, from A. Cairo's The Truthful Art.

Of course, eating chocolate alone will not magically make a nobel prize winner, but millions of readers thought "I like chocolate. I want to be smart." You can bet some fraction of those readers clicked the article, and probably went and ironically later bought chocolate.

For the majority of social and economic trends, it is impossible to identify with 100% certainty if a correlation does in fact reflect causation. To do so would require isolating individual variables, but doing so would significantly alter large groups of people's lives. You can argue that one factor causes another if several conditions are met. The cause has to precede the effect. In physics, this would be referred to as the influence cone. The two variables must show a strong, repeatable, correlation, and this correlation must be stronger than other variables which might explain the trend. Finally, the explanation must make sense.