An article headline claimed that "drugs cause homelessness" due to a positive relationship found between homeless populations and drug use. educated psychologists thought this might be flawed, because they thought unemployment was influencing both drug use and homelessness. this is an example of:

The answer is a third variable.

A third variable or a confounding variable is a variable that influences two separate variables that are being measured. In this case the two separate variables being measured are drug use and homeless populations, the third variable here would be unemployment.

answer; technology;

stable food supply,social structure, government,religion,culture/art,technology and writing/language;