Double Bar Graphs

(Comparative Bar Graphs)

Primary & Secondary Data

• Primary Data:– Information that is collected directly or first hand– Example: Data collected by you through a survey

• Secondary Data:– Information that is not collected first-hand– Example: Data from a newspaper or Census At

School (Canadian Statistics)

Discovery Activity• With your partner, complete the “Discovery

Activity” in the handout.

– Orally discuss the answers to questions 1-3– Write your answers to question 4

Exercise Vigorously Outside of School: 13-Year Old Canadian Males

8 10 12

24 22 24

05

1015202530

None About1/2 h

About1 h

About2-3 h

About4-6 h

7 h ormore

Time per Week

Perce

nt (%

)

Exercise Vigorously Outside of School: 13-Year Old Canadian

Females

1118 17

26

1612

05

1015202530

None About1/2 h

About1 h

About2-3 h

About4-6 h

7 h ormore

Time per Week

Perce

nt (%

)

Discovery Activity – Bar Graphs

Discovery Activity – Questions to Consider

1. List 3 things these graphs tell you.

2. A) Approximately what percent of 13-year-old males spend no time exercising vigorously outside of school?

B) Approximately what percent of 13-year-old males spend 7h or more exercising vigorously outside of school?

C) What is the most common amount of time spent exercising vigorously by 13-year-old males?

3. Repeat question 2 for 13-year-old females.

4. A) Compare the two bar graphs. What differences can you see between males and females regarding exercise habits? Justify your observations.

B) How could you make it easier to compare the two sets of data? Describe your ideas.

Easier to use a double bar graph?

Exercise Vigorously Outside of School: 13-Year Old Canadians

810

12

2422

24

11

18 17

26

16

12

0

5

10

15

20

25

30

None About 1/2 About 1 About 2-3 About 4-6 or more 7

Time per Week (Hours)

Pe

rce

nt

(%)

Males

Females

• 50 students in a junior high school were surveyed to find what their preferred mode of transportation is.

Girls

Mode of Transportation Number

Bicycle 15

Skateboard 6

Walking 9

Boys

Mode of Transportation Number

Bicycle 9

Skateboard 8

Walking 3

• Draw a double bar graph to show and compare the data in percent.

Calculating & Graphing Percents: Example

Calculating Percents• The total number of girls surveyed is 15 + 6 + 9 = 30

GirlsMode of

TransportationNumber Fraction Decimal Percent

Bicycle 15 15/30 15 ÷ 30 = 0.5 0.50 x 100% = 50%

Skateboard 6 6/30 6 ÷ 30 = 0.2 0.2 x 100% = 20%

Walking 9 9/30 9 ÷ 30 = 0.3 0.3 x 100% = 30%

Calculating Percents• The total number of boys surveyed is 9 + 8 + 3 = 20

BoysMode of

TransportationNumber Fraction Decimal Percent

Bicycle 9 9/20 9 ÷ 20 = 0.45 0.45 x 100% = 45%

Skateboard 8 8/20 8 ÷ 20 = 0.4 0.4 x 100% = 40%

Walking 3 3/20 3 ÷ 20 = 0.15 0.15 x 100% = 15%

• One reason to graph using percents is you can compare groups of data that have different sizes (e.g., girls – 30; boys – 20).

Graphing Percents

Preferred Mode of Transportation

50

20

30

4540

15

0

10

20

30

40

50

60

Bicylce Skateboard Walking

Mode of Transportation

Pe

rce

nt

(%)

Girls

Boys

Features you need for a double bar graph:• Different colours for the bars• Connect the bars in each category, with a space between

each category• Add a legend• Features of a regular bar graph (titles, intervals etc.)

Preferred Mode of Transportation

50

20

30

4540

15

0

10

20

30

40

50

60

Bicylce Skateboard Walking

Mode of Transportation

Pe

rc

en

t (%

)

Girls

Boys

Key Ideas

• A double bar graph shows how two or more groups of data compare.

• You can compare groups of data that have different sizes by using percents.