Causality and Correlation:

Often there may be a connection among 2 events: That is, when event happens, event B tends to happen.  However, this does not mean that A causes B; causality is not the same as correlation. An example is that statistics show a correlation between the expansion rate of grass and the consumption of gasoline. Does this mean that enlarged use of gasoline makes the grass grow? Unlikely. In fact, there is a separate, familiar, causal factor: Grass grows most in the spring and summer, when the weather  is best. The amount of travel by common in the United States increases in the summer, hence, the biggest gasoline consumption. The season is the fundamental factor. The message here is to make certain you are not mistaking correlation for causality: Be systematic.