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.
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