A researcher examines a bivariate relationship between x₁ and y and sees an association between the two variables. When they include a control variable, x₂, they suspect the variable is an intervening variable, What did they see happen to the relationship between x₁ and y when they included x₂?

Group of answer choices:

• relationship between x1 and y did not change
• relationship between x1 and y was different for different levels of x2
• relationship between x1 and y disappeared
• relationship between x1 and y became stronger