CHAPTER 8 Analyzing Bivariate Data We often find it telling to collect data that track two quantitative vari- ables simultaneously. We may want to look at changes in one variable as it changes with or perhaps even influences values of a second variable. How loosely or tightly connected two variables are can be quantified using the methods introduced in this chapter. One method, called regression analysis, explores whether we can improve our estimate of one variable by knowing the value of the other variable for an element of the popula- tion being studied. A unique benefit of regression analysis arises from the regression model itself: We can use the regression model to predict values of interest from information that is already known. By using recent information on automobile loan rates, for example, we can anticipate the rate we might qualify for as we decide what car to buy. Knowing how the rates have changed over time in recent weeks or even days, we can better