Section 2.2
Summer 2013 - Math 1040
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Roadmap
Plots of Various Data Types
We now describe chart types to qualitative and quantitative data. We will
skip dot charts, and later we return to scatterplots and time series.
Qualitative charts: Stem-and-leaf plot.
Quantative charts: Pie charts, Bar graphs / Pareto graphs.
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Stem And Leaf Plots
Like a histogram, a stem-and-leaf plot separates quantitative data into
somewhat natural classes. The advantage is that the numerical values are
retained. Below you can read the ages in years as 40, 47, 49, etc.
Age in years of the top 25 wealthiest people in the world.
The decimal point is 1 digit(s) to the right of the |
4
5
6
7
8
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0799
01246899
1237
13689
0447
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Stem And Leaf Plots
When the scaling is small, then zeros can be used as leaves.
Life spans (in days) of 40 house flies.
The decimal point is at the |
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6
8
10
12
14
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000
0000000
0000000000
00000000000
0000
00000
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Pie Charts
Qualitative variables in the nominal and ordinal forms, that take on a
reasonable number of values, in their basic forms can be organized with a
frequency table. Pie charts divide a circle’s area into sections representing
relative frequencies. That is, the area of the slices are proportional to the
frequencies.
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Pie Charts
Qualitative variables in the nominal and ordinal forms, that take on a
reasonable number of values, in their basic forms can be organized with a
frequency table. Pie charts divide a circle’s area into sections representing
relative frequencies. That is, the area of the slices are proportional to the
frequencies.
The central angle of a division of the pie is computed by:
Relative frequency × 360◦
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Pie Charts
City destination data:
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Pareto Charts
A survey is given to university students asking them about their primary
way of getting to campus (values include walking, cycling, taking a bus,
taking a train, driving a car, etc). This is nominal data, and we can record
the frequency for each value. A Pareto chart is suitable here.
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Pareto Charts
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Pareto Charts
Pareto charts require:
Bar height represents frequency or relative frequency.
Bars decrease in height from left to right.
Bars are spaced apart.
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Assignments
Assignment:
1
Read pages 53 - 54, 56 - 57.
2
Try exercises 1-5 odd, 9, 11 -19 odd, 23, 25, 35.
Vocabulary: Stem and leaf plot, pie chart, central angle, Pareto chart.
Understand: How and when it is useful to make a stem-and-leaf plot.
How and when it is useful to make pie charts, and bar graphs / Pareto
graphs.
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