A lagged correlation is used for when a time delay is suspected in the connection between the two variables. The sign of the time delay can point to he causality of the relationship. A correlation between two variables X and Y can mean four things:

• X affects Y,
• Y affects X,
• X and Y are affcted by a third variable Z, or
• the correlation was a coincidence.

A lagged correlation can sometimes eliminate the first or second connection.

The lag can ether be a single time delay, or a range. It is not allowed to vary both the starting month and the lag. Please contact me if you need a lag that is not in the long list.