Chapter 5 Bivariate Analysis

So far we have been concerned with making inference about a single population parameter. Many problems deal with comparing a parameter across two or more groups. Research questions include questions like:

  • Does the average life span differ across subspecies of a particular turtle?
  • Who has a higher percentage of the female vote - Democrats or Republicans?

A good way to think about all statistical models is that the observed data comes from some true model with some random error.


The MODEL is a mathematical formula (like \(y = f(x)\)). The formulation of the MODEL will change depending on the number of, and data types of explanatory variables. One goal of inferential analysis is to explain the variation in our data, using information contained in other measures.