The Art of Presenting Data:The Pie Chart or Circle Graph

What is it? How to Draw it

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What is a Pie Chart?

A pie chart or circle graph has sectors that visually display proportional parts of a total set of data that share a common variable

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Pie Chart Characteristics

1. Help an audience understand distribution of data quickly and easily.

2. Help to see how a total is divided into segments and percentages

3. Most effective when the number of segments is 10 or fewer

4. Especially useful with categorical data

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Marital Status Count %

(m of people) nrst 0.1 nrst 0.1Single 41.8 °Married 113.3 °Widowed 13.9 °Divorced 16.3 °

Total °

Source: US Census Bureau

Data on Marital Status from the US Census Bureau

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Categ DataTI for Pie Charts

• Get the raw data. Do a survey or read the data from a published survey

• Go to STAT, EDIT. Clear L1, L2, and L3• Input the raw categorical data into L1• Hit 2nd MODE, exiting to home screen.• Go to 2nd STAT. Use RIGHT ARROW key and

highlight MATH. ARROW DOWN to #5:SUM. Hit ENTER

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Categ DataTI for Pie Charts

• SUM( will appear on your home screen. Type 2nd 1 and hit ENTER. The sum of the raw data appears on your screen. Note it on paper

• Go to 2nd STAT:EDIT. ARROWs to the top of L2. Highlight L2. Type 2nd 1 total of the data. (L1data total). Hit ENTER.

• All the relative decimals will appear in L2.

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Categ DataTI for Pie Charts

• Highlight L3. Type 2nd 2 ● 100. Hit ENTER. This multiplies every decimal by 100 to get %ages for each pie sector.

• ARROWS to the top of L4. Highlight L4. Type 2nd 2 ● 360 (L2 ●360). Hit ENTER. This gives the ° you need to use with your protractor for each segment of the pie chart.

• Draw the pie chart using the data in STAT:EDIT

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Marital Status Count %

(m of people) nrst 0.1 nrst 0.1Single 41.8 22.6% 81.4 °Married 113.3 61.1% 220.0 °Widowed 13.9 7.5% 27.0 °Divorced 16.3 8.8% 31.7 °

Total 185.3 100.0% 360.0 °

Source: US Census Bureau

Answers for Totals, %ages, Angle Degrees

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Single22.6%

Married61.1%

Widowed7.5%

Divorced8.8%

Marital Status of Americans Ages 18 & Over

Source: US Census Bureau Sample Size: 185.3m Americans

Pie Chart Example

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Classwork & Homework

• Use the terms you’ve learned to create your own pie charts

• Answer some the ‘usual’ questions about the nature of this chart using the data and your powers of analysis.