1. Ch. 3 Histograms In a histogram, the areas of the blocks represent percentages. –Example: Ex. Set B #3 Types of variables: –Qualitative vs. quantitative Discrete vs. continuous –Example: Ex. Set D #1 Cross-tabulation –Example: Ex Set F #1

2. Any questions from HW? Categorical/qualitative variables: Values are groups and represent qualities or order –Examples: Smoking category (yes/no) Marital status (married, single, divorced, widowed) Year of college (1 st year, sophomore, junior, senior, FP)

3. Quantitative variables: Values that represent an amount. Can be discrete or continuous –Examples: Weight Number of cigarettes smoke/day Number of hours spent studying/day Red blood cell count

4. We use bar charts to represent categorical variables We can use stem-&-leaf plots to represent quantitative variables

5. Activity: Martin vs. Westvaco Background How to read the data Bar chart of categorical variables –Bar chart of pay categories by # of employees Stem & leaf plot –Plot of all ages Do Part I of activity How to divide ages (40 or 50 as division)

6. Histograms are only used for quantitative variables that are continuous. –Choose the width & endpoints of the intervals –Each bar has an area which represents a % –The bars touch –The height of each bar represents density

7. Histogram for age of laid off employees by 10 year intervals –Table (age int., count, percent, percent/year) –Draw the histogram What percent of 53 year olds were laid off? What percent of 53-55 year olds were laid off?

8. BEWARE Usually all intervals are equal, but you must watch out for those that are not created equally. (Ch. 3 Review Exs. #2, 4)