Used to describe the observed relationship between instances of two events. A systematic pattern can be seen in the occurrences of events that are correlated. When the events involve numbers, a positive correlation means that as one increases, the other increases as well. A negative correlation means that as one increases, the other decreases. Correlation does NOT imply causation in any way. In other words, just because two events are correlated does not mean that one causes another, or has anything to do with the other – correlations deal only with observed instances of events, and any further conclusions cannot be inferred from correlation alone. Strong correlation, however, does often warrant further investigation to determine causation.