Scatterplots&

Correlation

What is a scatterplot?

A scatterplot is a graph of points used to show the relationship between two sets of data

Bivariate data is two sets of variables measured in a single experimental unit

When making a scatterplot remember to…

Label variables

Give values of variables

Keep constant intervals on graph

Do NOT connect dots

ExamplesGood or bad? Good or bad?

Your turn!Create a scatterplot for the relationship between

height and weight.

Height (x)

5’9 6’3 5’4 6’1 6’0

Weight (y)

125 152 103 145 140

Correct graph

Relations between X and Y

No Correlation

http://mste.illinois.edu/courses/ci330ms/youtsey/scatterinfo.html

CorrelationStrong, weak or none?

http://allpsych.com/researchmethods/correlation.html

What is an Outlier?

An outlier is a number that is distant from the set.There can be numerous outliers.There can be no outliers.

Find the outlier(s) using a table.

x 1 1 4 2 3 1 6 5 3

y 10 9 26 15 21 2 35 40 20

Find the outliers using a graph

Draw A Scatterplot.Find outliers.

Find correlation.

Study time (x) vs. grades (y)

x 1/2 3/4 3 7 5 2 4 2 6 1 0

y D+ C- B+ A+ A D- B+ A+ A- C F

Correct Answer

Real World UseUS population vs. time

US population from 1790-1940year pop (millions)1790 3.9291800 5.3081810 7.2401820 9.6381830 12.8661840 17.0691850 23.1921860 31.4431870 38.5581880 50.1561890 62.9481900 75.9951910 91.9721920 105.7111930 122.7751940 131.410

Reference: Pearl, R., Reed, L. J. and Kish, J. F. (1940), The logistic curve and the census count of 1940; Science, vol 92, no. 2395, pp. 486-488.

What We LearnedWhat scatterplots are used for.

How to plot on a scatterplot.

Different types of correlation.

How to find outliers.

How scatterplots are used worldwide.