Explain the following: Categorical - classify observations into named categories, e.g., HIV status classified as "positive" or "negative" Ordinal - categories that can be put in rank order e.g., Stage of cancer classified as stage I, stage II, stage III, stage IV Quantitative - true numerical values that can be put on a number line - e.g., age (years) - e.g., Serum cholesterol (mg/dL)