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What is a histogram?
• A histogram is a type of bar graph whose bars represent the frequencies of NUMERIC DATA within intervals.
Y-Axis has the frequency
X-Axis has the intervals
Intervals
• You need to look at your data and decide your intervals. This is similar to a stem-and-leaf plot because of the intervals.
• Example: Amy lists her quiz scores. This is her list: 88, 95, 75, 72, 95, 96, 85, 83, 84, 80, 70, 92
• What intervals would you chose?
Stem-and-Leaf Plot• Example: Amy lists her quiz scores. This is her
list: 88, 95, 75, 82, 95, 96, 85, 83, 84, 80, 70, 92• The intervals could be 70-79, 80-89, and 90-99.• The stem-and-leaf plot would look like this:
Stems Leaves
7
8
9
0 5
0 2 3 4 5 8
3 5 5 6
Frequency Tables• Once you have your
intervals decided, make a frequency table.
• Frequency – the amount of times it occurs
• Example: Amy lists her quiz scores. This is her list: 88, 95, 75, 82, 95, 96, 85, 83, 84, 80, 70, 92
Intervals Frequency
70-79
80-89
90-99
Creating a histogram!
Intervals Frequency
70-79 2
80-89 6
90-99 4
Title:
Freq
uenc
y
Label:Intervals:
What observations can you make about the distribution of the data?
Stem-and Leaf Plot vs. Histogram• How are they similar? How are they
different?
Stems Leaves
7
8
9
0 5
0 2 3 4 5 8
3 5 5 6
Title: Amy’s Quiz Scores
Freq
uenc
y
Label: Quiz GradesIntervals: 70-79 80-89 90-99
6
5
4
3
2
1
0
Things to remember:• You will use NUMERIC DATA.• You decide intervals based on the data. It
does not always have to be in tens.• Must be constructed from a frequency table.• All bars must touch and be the same width.
• X-Axis has intervals and a label.• Y-Axis has frequencies.• You need to have a title.
Your turn!• Students were surveyed and asked how many
hours they play outside each week. They said: 6, 9, 4, 5, 0, 7, 1, 5, 4, 8, 3, 2, 2, 3, 2, 4, 9, 4, 0,
Title:
Freq
uenc
y
Label:
Intervals Frequency
Intervals:
How did you do?• Students were surveyed and asked how many
hours they play outside each week. They said: 6, 9, 4, 5, 5, 7, 1, 5, 4, 8, 3, 2, 2, 3, 2, 4, 9, 4, 0, 8
Title: Playing Outside
Freq
uenc
y
Label: Hours Outside
Intervals Frequency
0-1 2
2-3 5
4-5 7
6-7 2
8-9 4 Intervals: 0-1 2-3 4-5 6-7 8-9
12
10
8
6
4
2
0
Histograms
• What observations can you make about the distribution of the data in your histogram?
• How can a histogram be helpful to you?
• What things do you need to watch out for when making a histogram?
What is a percent bar graph?• A percent bar graph is a type of bar graph where
you graph relative frequencies to help you visualize how the data is distributed for CATEGORICAL DATA.
Y-Axis has the RelativeFrequency (%)
X-Axis has the categories
Make a Table• Example: Sue asked her 25 classmates what
their favorite color was. 4 people said green, 6 people said purple, 5 people said pink, 7 people said blue, and 3 people said yellow.
Favorite Colors
Color Green Purple Pink Blue Yellow
Frequency
Relative Frequency Table• To make a percent bar graph, you need to
know the relative frequency of each category.• Relative Frequency – the ratio of the
frequency to the total as a fraction or percentFavorite Colors
Color Green Purple Pink Blue Yellow
Frequency 4 6 5 7 3
Relative Frequency
4 ---- = ----25 100
6 ---- = ----25 100
5 ---- = ----25 100
7 ---- = ----25 100
3 ---- = ----25 100
Creating a percent bar graph!Title: Favorite Colors
Rela
tive
Freq
uenc
y (%
)
Categories: Green Purple Pink Blue Yellow
What observations can you make about the data?
Color Green Purple Pink Blue Yellow
Frequency 4 6 5 7 3
% 16 24 20 28 12
30
25
20
15
10
5
0
Label: Color
Creating a percent bar graph!Title: Favorite Colors
Rela
tive
Freq
uenc
y (%
)
Categories: Green Purple Pink Blue Yellow
What observations can you make about the data?
Color Green Purple Pink Blue Yellow
Frequency 4 6 5 7 3
% 16 24 20 28 12
30
25
20
15
10
5
0
Label: Color
Things to remember:• You will use CATEGORICAL DATA.• You need to make a relative frequency table.• The percentage is the frequency out of the
whole. You need to get to 100%.• All bars must touch and be the same width.
• X-Axis has categories and a label.• Y-Axis has relative frequencies (percents).• You need to have a title.
Your turn!Title:
Rela
tive
Freq
uenc
y (%
)
Categories:
What observations can you make about the data?
Elective Art Band Orchestra Theatre
Frequency 10 18 14 8
%
0
Label:
When I went to lunch, I asked people what their elective was. Their answers are in the table.
How did you do?Title: Elective Classes
Rela
tive
Freq
uenc
y (%
)
Categories: Art Band Orchestra Theatre
What observations can you make about the data?
Elective Art Band Orchestra Theatre
Frequency 10 18 14 8
% 20 36 28 16
Label: Elective Class
When I went to lunch, I asked people what their elective was. Their answers are in the table.
40
30
20
10
0
Percent Bar Graph
• What observations can you make about the data in your percent bar graph?
• How can a percent bar graph be helpful to you?
• What things do you need to watch out for when making a percent bar graph?