Lesson 2.5: Look for Covariation
Lesson
Introduction ![]250:l The last lesson introduced several ways to analyze data depending on the kind of question under investigation. In this lesson we look at one kind of question, about relationships, or covariation, in more detail. For example: Is there evidence of a relationship between fish weight and mercury in muscle tissue? In other words, as one attribute increases, does the other attribute also change in one direction or another? Some students in sixth grade become familiar with graphing two variables in two-dimensional space with X and Y axes. But analysis and interpretation of bivariate relationships is a focus in grade 8, when students learn to recognize and interpret patterns in scatter plots in the context of questions about relationships. Eighth graders learn to quantify direction and strength of a relationship using the equation for a best-fit line, and what those properties imply about real-world phenomena. Key Ideas for Students: Use a scatter plot to look for covariation between two numerical attributes Distinguish positive and negative correlation (or no correlation) Distinguish ‘strong’ and ‘weak’ correlation Recognize whether a relationship is linear or nonlinear Plot a best-fit line, and interpret what the equation says about the nature of the relationship Recognize that correlation does not necessarily mean one factor causes the other
Topics and standards: Correlation