# Worksheet 9: Correlation

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1. Brainstorm ideas for quantitative measurements we could use for the strength of association between two variables.


2. Why does the slope of the best-fit line change when you change the units of the data?


3. Variability and the slope of the best-fit line.
    a. What is the slope of the line between the points $(0,0)$ and $(100,1)$? 
    

    b. Explain why if the variable $X$ varies in the range of $0$ to $100$, and $Y$ varies in the range $0$ to $1$, then the slope of the best-fit line will probably never get close to 1.
    

4. Explain why in a standardized dataset:

    a. The mean is **0**
    
    b. The standard deviation is **1**
    
    c. The data is **unitless**
    


5. If $X$ and $Y$ are correlated, can we infer that $X$ causes $Y$ or that $Y$ causes $X$?