Correlation
A measure from −1 to +1 of how closely two assets move together. Positive means they tend to rise and fall in step; negative means they move oppositely.
Correlation must be computed on returns, not on prices. Two assets that both drift upward over a year will show a high price correlation whether or not their day-to-day moves have anything to do with each other. Our comparison pages use daily returns, and we require a minimum overlapping history before publishing a figure.