A popular cell phone company is investigating whether ethnicity (labeled as A, B, C, D) and age (labeled as Y, M, W) are factors which explain how much people spend on cell phone bills. What is the purpose of this investigation?
1) To determine if there is a correlation between ethnicity and cell phone bill spending
2) To determine if there is a correlation between age and cell phone bill spending
3) To determine if there is a correlation between ethnicity and age
4) To determine if there is a correlation between ethnicity, age, and cell phone bill spending