Correlation vs. Causation

I think the first thing people think of when talking about correlation and causation is that they are the same thing. But they really aren't. Correlation, according to dictionary.com, is  the extent of correspondence between the ordering of two variables. Correlation is positive or direct when two variables move in the same direction and negative or inverse when they move in opposite directions. Causation on the other hand, is when two variables directly effect one another. For example, in you put your dog outside at night and it gets sick, it is likely that it got sick from being put outside. However, the cause of it getting sick could be a virus or a bacteria. 

If one action causes another, then they are most certainly correlated. But just because two things occur together does not mean that one caused the other. For example, many studies are actually designed to test a correlation, but are suggestive of “reasons” for the correlation. People learn of a study showing that “girls who watch soap operas are more likely to have eating disorders” — a correlation between soap opera watching and eating disorders — but then they incorrectly conclude that watching soap operas gives girls eating disorders. 

The most effective way of establishing causality is through a controlled study. In a controlled study, two groups of people who are comparable in almost every way are given two different sets of experiences, and the outcome is compared. If the two groups have substantially different outcomes, then the different experiences may have caused the different outcome.  

Without clear reasons to accept causality, we should only accept correlation. Two events occurring in close proximity does not imply that one caused the other, even if it seems to makes perfect sense.