1. 3.2 Correlation Pg

2. Correlation
Measures the direction and strength of the linear relationship between two quantitative variables.
Usually written as r.

3. The correlation coefficient r
Is defined as:
𝑟= 1 𝑛− 𝑥 𝑖 − 𝑥 𝑠 𝑥 𝑦 𝑖 − 𝑦 𝑠 𝑦
Where we have data on variables x and y for n individuals.
See pg #3.24

4. How to interpret correlation…pg. 143-144
Correlation makes no distinction between explanatory and response variables. Doesn’t matter what you call x or y when calculating correlation.
Correlation requires both variables be quantitative.
Because r uses standardized values, r does not change when we change units of measurement of x, y, or both. r itself has no unit of measurement, it is just a number.
Positive r indicates positive association and negative r indicates negative association

5. Interpretation continued
Correlation r is always a number between -1 and 1. values near 0 indicate a very weak linear relationship.
Values close to -1 or 1 indicate that points in a scatterplot lie close to a straight line.
Correlation measures the strength of only linear relationships
Like mean and standard deviation, correlation is not resistant. r is strongly affected by outlying observations.

6. Complete the following problems Starting on page 129:
Assignment
Read pg
Complete the following problems Starting on page 129:
#3.10, 3.11, 3.12, 3.15, 3.25, 3.30