A researcher obtained the average SAT scores of all students in each of the 50 states, and the average teacher salaries in each of the 50 states. She found a negative correlation between these variables. The researcher concluded that a lurking variable must be present. By lurking variable, she means a variable that is not among the variables studied but which affects the response variable. the true cause of a response. any variable that produces a large residual. the true variable, which is explained by the explanatory variable.