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Correlation and Causation Part I – Scatterplots
Correlation and CausationPart I – Scatterplots
This video is designed to accompany
pages 19-24in
Making Sense of UncertaintyActivities for Teaching Statistical
ReasoningVan-Griner Publishing Company
cor·re·la·tion[ kàwrə láysh'n ] 1. mutual or complementary relationship: a
relationship in which two or more things are mutual or complementary
2. relatedness of variables: the degree to which two or more variables are related and change together
Vernacular
Variables: Height and Weight
Bigger values of Height tend to be associated with bigger values of Weight.
Example
A scatterplot of height (y-axis) versus weight (x-axis) would likely look something like this.
Scatterplot
Other Scatterplots Plots! Oh No!
Quiz Average
Fina
l Exa
m
Scor
e
Time Spent Studying
Stud
ent
Gra
des
Hours Exercised
LDL
Leve
ls
GNP per capita
Life
Exp
ecta
ncy
at
Birt
h
Language of Association
1. positive association - points have an upward trend from left to right
2. negative association - points have a downward trend from left to right
3. 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.
Scatterplots Revisited
Plots! Oh Yeah!
Time Spent Studying
Stud
ent
Gra
des
Positive
Modera
tely S
trong
Quiz Average
Fina
l Exa
m
Scor
e
Not Very StrongGNP per capita
Life
Exp
ecta
ncy
at
Birt
h Positive
Arguably Pretty
StrongNot Straight Line
Hours Exercised
LDL
Leve
ls
NegativePretty Strong
Scatterplots 1. Visual way of assessing association, both
direction and strength.
2. Makes sense as long as you have two variables that you can display in a scatterplot
Using Your Eyes
Association Between Gender and Hours Spent Doing Homework
What do you see?
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.
