Negative correlation occurs when one variable moves above its moving average while the second moves below its moving average.

FORBES: Basics of Asset Allocation (Part 2 of 2)

Positive correlation occurs when one variable moves above its moving average while the second also moves above its moving average.

FORBES: Basics of Asset Allocation (Part 2 of 2)

Studies such as this one, which rely on correlating one variable with another, are not enough to draw firm conclusions on their own, since correlation is not necessarily causation.

ECONOMIST: Diet and the unborn child