2.2 Presenting Data in Charts

Data

Data

Pie Chart

Pie Chart

Histogram

Histogram

Numerical Data

Numerical Data

Bar Chart

Bar Chart

Categorical Data

Categorical Data

2.2.1 Bar Chart

Bar charts are used for categorical data. Recall in 2.2.1, we have the following frequency and relative frequency table:

Degree

Frequency

Relative Frequency

Bachelors

6

0.3

Law

3

0.15

Masters

2

0.1

MBA

7

0.35

None

1

0.05

PhD

1

0.05

Total

20

1

In the following chart, the bottom horizontal line represents degree and the left vertical line represents frequency. The heights of the bars represent the frequencies.

A bar chart for the relative frequency distribution is as follows:

We can also add data values to the bars as follows:

2.2.2 Pie Chart

Pie Charts are also used for categorical data. A pie chart is a circle divided into sections. Each section represents a category. The area of each sector is proportional to the percentage of the category. Recall in 2.2.1, we have the following percentage distribution:

Degree

Percentage (%)

Bachelors

30

Law

15

Masters

10

MBA

35

None

5

PhD

5

Total

100

A pie chart for the percentage distribution is as following:

2.2.3. Histogram

Histograms are used for numerical data. A histogram looks similar to bar graph. However there is a major difference between these two charts. A histogram has no gap between two adjacent bars, but a bar graph has gap. (A gap can occur to a histogram if there is no frequency for a class interval.)

Recall in 2.2.2, we have the frequency and relative frequency table as following:

Monthly electricity bill

Frequency

Relative Frequency

40 – 59

4

0.2

60 – 79

6

0.3

80 – 99

3

0.15

100 – 119

3

0.15

120 – 139

2

0.1

140 – 159

2

0.1

total

20

1

A histogram for the frequency distribution is as follows:

40 60 80 100 120 140 160

40 60 80 100 120 140 160

Or

40-59 60-79 80-99 100-119 120-139 140-160 160

40-59 60-79 80-99 100-119 120-139 140-160 160

Note: We use the above example to explain why we do not need gaps between adjacent bars. For the above histograms, the bottom horizontal line is a scale (between 40 and 160). The class intervals 40-59, 60-79, 80-99, 100-119, 120-139 and 140-149 are placed according to the scale, and the intervals are supposed to touch each other. For the first class interval, we write 40-59 instead of 40-60 because we want to show that it does not include 60. But it does not mean that we need to show a gap between 59 and 60.

2.2.4 Clustered, Stacked, and 3-D Bar Graphs

Example The following data represent the education attainment of males and females 25 years and older in 2003.

Education Attainment

Males (in millions)

Females (in millions)

Not a high school graduate

14.1

14.5

High school graduate

27.4

31.9

Some college, no degree

15.2

16.6

Associate’s degree

6.4

8.8

Bachelor’s degree

16.4

16.9

Advanced degree

9.2

7.9

We can use the following bar charts to present the data:

Clustered bar graph

Clustered bar graph

Stacked bar graph

Stacked bar graph

3-D bar graph

3-D bar graph

2.2.5 Line

Example The following data represent the number of bachelor’s degrees in engineering awarded from 1999-2003:

Year

Degrees Awarded

1999

62,372.00

2000

63,731.00

2001

65,113.00

2002

67,301.00

2003

70,949.00

The left chart below uses lines to present the data. The right chart below uses bars to present the data. Both charts show the trend of the number of degrees from 1999-2003.

Example The following are high and low temperatures in Meridian, December 21-300, 2018:

High temperature

Low temperature

21-Dec

46

33

22-Dec

62

30

23-Dec

70

41

24-Dec

58

34

25-Dec

69

34

26-Dec

67

45

27-Dec

64

56

28-Dec

65

49

29-Dec

56

44

30-Dec

65

50