Describing Relationships (Program 8)

1. Scatter plot
2. Categorical variable (also called "dummy variables")
3. Least squares regression line

Scatter plot

• manatee deaths vs number of power boat registrations, 1977-87.
• response variable: manatee deaths
• explanatory variable: number of power boat registrations
• 1 case: (point, year)
• positive (negative) association
  
• fluoride level: explanatory variable
• number of cavities: response variable
• city size: categorical variable (we call categorical variables "dummy variables")

Median trace to look for trends in scatter plot (A Median Trace is similiar to a Moving Average)

• draft number vs birth data lottery
• least squares line: minimizes sum of the square of the residuals

Regression

• obesity: relationship between metabolism and body weight
• look at Lean Body Mass vs Metabolic Rate

Be careful of extrapolation and outliers (influential observations)

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