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# Scatterplot

• Study the relationship between two quantitative variables.

# Scatterplot

• Form: linear or non-linear?
• Direction: positive or negative?
• Strength: strong or weak?
• Outliers?

# Linear Regression

• Find a straight line to fit the relationship between $X$ and $Y$
• Also used to predict $Y$ for a given $X$

# Regression Equation

• $\hat{y}=b_0+b_1 x$

# Check the Assumptions

• Data coming from SRS
• Variables linearly related (Scatterplot)
• Normality of $Y$ (PP-plot)
• Same standard deviation at all $X$ values (Residual plot)

# Residual Plot

• Residual = $y$ - $\hat{y}$