1. What is the difference between quantitative data and categorical data?
HISTOGRAMS
What is the difference between quantitative data and categorical data?

2. HISTOGRAMS
Categorical data consists of observations that can be separated into categories. Examples include favorite sport, favorite type of automobile, what state a person was born in, etc. Circle graphs or pie charts are often used to display the data. An example follows.

3. Circle Graphs or Pie Charts
A pie chart is often used to plot categorical data when the choices are nonnumeric.

4. HISTOGRAMS
Quantitative data consists of observations that have numerical values. Examples include the price of a gallon of gasoline, the ages of your classmates, and the heights of buildings in a city. This data is often displayed in bar graphs or histograms. An example follows.

5. Histograms
Histogram
A bar graph plot of the data, with the bars placed adjacent to each other.

6. Histograms
Characteristics of data detected by histograms

7. Histograms
Characteristics of data detected by histograms

8. Histogram Example
Table 2.8 gives the birth rates (per population) in each of the 50 states of the United States. Plot these data in a histogram.

9. Histogram Example Solution
Since the data range from a low value of 12.4 to a high of 21.9, let us use class intervals of length 1.5, starting at the value 12.
With these class intervals, we obtain the following frequency table.
A histogram plot of these data is presented as follows.

10. Individual Practice
The following data set represents the scores on intelligence quotient (IQ) examinations of 40 sixth-grade students at a particular school:
114, 122, 103, 118, 99, 105, 134, 125, 117, 106, 109, 104, 111, 127,
133, 111, 117, 103, 120, 98, 100, 130, 141, 119, 128, 106, 109, 115,
113, 121, 100, 130, 125, 117, 119, 113, 104, 108, 110, 102
(a) Present this data set in a histogram. Use intervals of 10.
(b) Which class interval contains the greatest number of data values?
(c) Is there a roughly equal number of data in each class interval?
(d) Does the histogram appear to be approximately symmetric? Why?