Be cautious when there’s some, be cautious when there’s none, and be cautious when adding more than one.
What do the heck does that mean???
Let’s take these correlation cautions one by one.
Be cautious when there’s some. Suppose you did a study and found a correlation between job performance and high school grades. Does this mean that if we simply increase everyone’s high school grades that they will perform better at work??? Clearly not!