system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Correlation vs. Causation 

When looking at statistical data over a period of time, what does “correlation” mean?  How is it different from “causation?”
gpt
In this context, correlation would mean that two things track with each other. If X goes up, so does Y, and if X goes down, so does Y. Not necessarily at the same rate. There is another type of correlation, called inverse correlation, that is where when one thing goes up, the other goes down, not necessarily at the same rate. X goes up, Y goes down and X goes down, Y goes up.

Correlation is different from causation because from the data you can't tell that X causes Y, although it might. This is obvious when you realize that if X correlates with Y, the reverse is true, Y correlates with X, yet very rarely does X cause Y *and* Y cause X.

As an example, sales of ice cream rise in the summer, as would deaths from drowning (because more people swim in the summer). So ice cream sales and drownings are correlated. But that does not mean that drowning causes ice cream sales, or ice cream causes drowning.

**Edit: Added explanation of Inverse Correlation**