Statistics Question

A correlation exists between two variables when the higher values of one variable consistently go with the higher
values of another variable, or when the higher values of one variable consistently go with the lower values of
another variable. A scatter diagram (or scatterplot) is a graph in which each point represents the values of the
two variables.
A correlation coefficient (r) is a number between -1 and 1. It describes the strength of the correlation between
two variables. The strongest linear relationship is indicated with a correlation coefficient (r) equal to -1 or 1. In
this case, the points would all lie on a line. The weakest linear relationship is indicated with an r=0. In this case,
the points would all be scattered.  

Possible Explanations for a Correlation
 1) The correlation is coincidence.
 2) Both variables might be directly influenced by some common underlying cause.
 3) One variable may be a direct cause of the other. 

Negative correlation: One variable increases while the other decreases.