Correlation is not causation (idea)

Very important to remember when applying any sort of social science, such as psychology.

Both my high school and college psych courses provided me with the 'ice cream causes drowning' example:

Drowning deaths are most frequent during the months when ice cream sales are at their peak.

From this fact alone, one can make the causality go two ways:

1. By eating ice cream, you are more likely to get a cramp and drown while swimming.
2. When people drown, the mourners are more likely to console themselves by going out for ice cream.

Both of these theories are pretty shaky. What is more likely is that we did not look at enough information:

3. During the summer, more people are likely to go swimming, and drown. People are also more likely to buy ice cream.

In this model, note that drowning and ice cream sales do not effect each other, but both are effected by a common cause.