Correlation and Causation Part I – Scatterplots 1

This video is designed to accompany pages 19-24 in Making Sense of Uncertainty Activities for Teaching Statistical Reasoning Van-Griner Publishing Company 2

Vernacular cor·re·la·tion [ kàwrə láysh'n ] mutual or complementary relationship: a relationship in which two or more things are mutual or complementary relatedness of variables: the degree to which two or more variables are related and change together 3

Example Variables: Height and Weight Bigger values of Height tend to be associated with bigger values of Weight. 4

Scatterplot A scatterplot of height (y-axis) versus weight (x-axis) would likely look something like this. 5

Life Expectancy at Birth Other Scatterplots Plots! Oh No! Time Spent Studying Student Grades Hours Exercised LDL Levels GNP per capita Life Expectancy at Birth Quiz Average Final Exam Score 6

Language of Association positive association - points have an upward trend from left to right negative association - points have a downward trend from left to right strength - points are tightly clustered about some clear pattern (maybe straight line) Often the word “correlation” is used interchangeably with “association.” That’s OK until we get more technical. 7

Life Expectancy at Birth Scatterplots Revisited Plots! Oh Yeah! Time Spent Studying Student Grades Hours Exercised LDL Levels Negative Pretty Strong Moderately Strong Positive GNP per capita Life Expectancy at Birth Quiz Average Final Exam Score Positive Arguably Pretty Strong Not Straight Line Not Very Strong 8

Using Your Eyes Scatterplots Visual way of assessing association, both direction and strength. Makes sense as long as you have two variables that you can display in a scatterplot 9

Association Between Gender and Hours Spent Doing Homework What do you see? 10

One-Sentence Reflection Simple scatterplots are an informal, but useful visual means of addressing both the direction and strength of the relationship between two variables that are appropriate for this kind of plot.