thedegree of relatedness between two sets of scores. If twosets of scores are correlated, it enables researchers topredict (with varying degrees of certainty) the approximatevalue of one score if they know the value of the other. Apositive correlation exists when high values on onevariable are associated with high values on anothervariable. A negative correlation exists when highvalues on one variable are associated with low values onanother variable.
this phenomenon arises in some drug categories, such as theopiates (heroin, morphine etc) and tryptamines (LSD,mescaline and psilocybin) when the prolonged use of one drugin the group results in the development of tolerance to theothers opioids.