What is a variable interaction? Simply put, it is when the setting for one variable in your test positively or negatively influences the setting of another variable. If they have no effect on each other, they are said to be independent. In a positive interaction, two (or more) variables create a synergistic effect (yielding results that are greater than the sum of the parts). In a negative interaction, two (or more) variables undercut each other and cancel out some of the individual effects.
The Drunk Who Lost His Car Keys
A policeman on patrol noticed a man on all fours crawling around under a streetlamp in the middle of the night. After stopping to take a closer look, the policeman quickly determined that the man was ...