Pie charts

Pie chart is a circular graph where a circle is divided into sections each representing a frequency of each item in the data set.

A pie chart shows the relative contribution that different categories contribute to an overall total. They are generally used to show percentage or proportional data and the percentage represented by each category is provided next to the corresponding slice of pie. The total of all the percentages shown in the pie chart should be 100.
They are good for displaying data for around 6 categories or fewer. When there are more categories it is difficult for the eye to distinguish between the relative sizes of the different sectors and so the chart becomes difficult to interpret. 

To draw a pie chart, the total frequency is equated to the 360^o angles that makes a circle. So the frequency of each item is presented by a sector of the circle whose angle is a fraction of the total frequency.

Example

Consider the following Data that shows the favorite game for some grade 8 students .

Games	Number
Soccer	400
handball	50
Basketball	60
Volleyball	250
Athletics	300

Required: Presenting this data in a pie chart

solution

We need to find the size of the sectors in our desired circle chart that will represent each frequency.

The total frequency =400+50+60+250+300 = 1060

The radius of the circle chart does not matter, it can be of any size but make sure you select the one that is most convenient and will make your char presentable.

we equate: 1060 students = 360^o

the sector that will represent the soccer will be (400/1060)*360 = ~136^o

sector for handball = (50/1060) *360 = ~17 ^o

sector for basketball =(60/1060) * 360 = ~20^o

sector for volleyball = (250/1060) * 360 = ~85^o

sector for athletics = (300/1060) * 360 = 102^o

note that we have approximated the angles to whole numbers but when you add them they should add up to 360^o . that is (136 + 17 +20 +85+102)=360.

we should use the radius of the circle as a reference line from which we will draw sectors of the circle. The pie chart after you draw it should resemble the following chart

Related pages

• Introduction to statistics
• Line graphs
• Grouped and ungrouped data
• Frequency polygon
• Histograms
• Measures of Central tendency
• Mean for grouped data
• Working with the assumed mean
• Quartiles, Deciles and percentiles
• Measures of dispersion
• Variance
• Bar Graphs
• Grouping Data

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