Correlation of a Scatter Plot

What is correlation… O It describes the direction and strength of a straight-line relationship between two quantitative variables. O You cannot calculate correlation for curved graphs.

Correlation is described by the variable r O A value close to +1 has a strong positiv e correla tion O A value close to -1 has a strong negativ e correla tion O A value close to 0 has a weak or no correla tion Its range of value is -1 to + 1

Examples of Correlation Values

The Formula to Calculate It

Some interesting facts 1. The correlation value does not change if the measurement units change (i.e., meters vs. yards) 2. Correlation ignores the distinction between explanatory and response variables. Why?

The Answer… O If the places were switched and instead of both rising they were both going down, it’s still a positive correlation.

Why does he have an effect on correlation? Outliers can change a correlation value from strong to weak.

O The number of convertibles sold at a car dealership in a month and the average monthly temperature (degrees Fahrenheit). O Draw the scatterplot, find each Σ value and the value for r (correlation value). Round all answers to 2 decimal places. Group Activity Convertibles sold (x) Avg. Monthly temp. (y)