Pie chart
A pie chart (if spatially: cake or pie chart ) is a representation form of part of a whole values as parts of a circle. The pie chart is circular and divided into several pie sectors , with each pie sector representing a partial value and the circle thus the sum of the partial values (the whole). The alternative designation as pie or pie chart refers to sections of a round cake that correspond to the sectors of the circle.
history
The first known use of pie charts can be found in William Playfair's (1759–1823) publication "The Statistical Breviary" from 1801. The Scottish engineer and economist Playfair used this form of representation in his work to determine the territorial division of the Turkish Empire To clarify continents.
In the following time, this form of representation received little attention. The French engineer Charles Joseph Minard took it up again in 1858 to add a third dimension to the representation of information. Since then, many variations of the pie chart, such as: B. polar, area, radar, pie or 3D diagrams designed. The most common form, however, is still the simple representation as a pie chart.
Properties and creation
Pie charts are often used to show distributions and proportions. The number of partial values should not be more than 7, otherwise the diagram will be confusing. Several small partial values are also displayed in a confusing manner. In this case, it is advisable to combine the small partial values to form an “other” value. The clarity usually increases when the partial values are sorted according to size in a clockwise direction and the largest partial value begins on the 12 o'clock line, as with a clock.
Pie charts can be used e.g. B. with the help of a spreadsheet .
The sectors of the circle are each defined by radius lines from the edge to the center. The center angle between two adjacent radius lines determines the size of the sectors of the circle. The respective sector size (as an angle) is calculated as follows:
The radius of the circle is arbitrary; the calculated angles remain the same.
Different colors, patterns and shades are used to better distinguish the respective sectors.
Outside of scientific operations, pie charts can be found in many external and internal company presentations. In addition, journalists also use the pie chart to make the size relationships between groups, parties, affected persons or the like clear, so that pie charts can be found again and again in newspapers and magazines.
Variations
Donut chart
Exploded illustration
Semicircle diagram
Polar area diagram
Donut chart
A special form of the classic pie chart is the ring chart. A donut chart shows value data as a percentage of the whole. Categories are represented by individual segments. Donut charts are typically used to show percentages. While the pie chart only offers the option of displaying one data series, two or more data series can be illustrated or compared with one another in the ring chart. The open area in the middle of the diagram is often used to insert a comment.
Exploded illustration
In principle, the exploded representation of the structure of the diagram can be compared with the conventional representation. However, some segments are moved a little out of the middle, so that there are gaps between the individual segments. This effect is used to draw attention to a specific part of the diagram. The exploded representation is used in both the pie chart and the ring chart.
Semicircle diagram
Semicircular diagrams are often used to visualize the distribution of seats in a parliament. The semicircle represents the total number of seats. The majority distribution can be read from the individual sectors. The representation as a semicircle can be traced back to the usual allocation of the parties in the left-center-right scheme.
Polar area diagram
This type of visualization is used to display cyclically recurring phenomena. This type of diagram can be traced back to Florence Nightingale . In 1858 she presented the connection between deaths and hygiene conditions.
criticism
The pie chart is not suitable for displaying data at any scale level. It is often used in the representation of discrete data. It is therefore particularly recommended for the nominal and ordinal scale levels, but makes little sense for the interval and ratio scales. This has the disadvantage of one-dimensionality. The user can display only one data series, that is, one row or column, in a pie chart. If you want to compare two results, you need to create two pie charts. Pie charts quickly become confusing as the number of characteristic values increases. As a rule of thumb, a pie chart is confusing for more than seven occurrences. It is particularly useful as a comparison between two distributions in which the differences become very clear. However, the representation of a distribution by means of a three-dimensional circle diagram should be completely dispensed with. The color scheme of the circular sectors can also lead to a distorted perception. For example, a clumsy color choice for individual segments can accentuate part of the distribution unintentionally. In the eyes of the beholder, a colored segment of a circle appears disproportionately large. Use of a pie chart should only be considered when there is only one data series, no negative values, zero zero values, and the categories represent parts of the entire pie chart.
example
A department store manager wants to display the distribution of purchases across the department in a pie chart. Of the 95 shopping files, 32 were in the grocery department. The corresponding sector of the pie chart is calculated as follows:
The sector for sales in the grocery department must be 121.26 degrees. The calculation of the angular degrees for the other departments is shown in the table below (relative proportions and angular degrees to two decimal places, sum of the angular degrees rounded to one decimal place).
| Department | Number of purchases | Degrees of angle (°) | Relative share (%) |
|---|---|---|---|
| Food | 32 | 121.26 | 33.68 |
| Women's clothing | 21st | 79.58 | 22.11 |
| Toys | 12 | 45.47 | 12.63 |
| Children's clothing | 11 | 41.68 | 11.58 |
| Electrical appliances | 10 | 37.89 | 10.53 |
| Men's clothing | 9 | 34.11 | 9.47 |
| All in all | 95 | 360 | 100 |
literature
- Bühner, Ziegler: Statistics for psychologists and social scientists . 1st edition. Pearson Studies, 2009.
- Dolic: Statistics with R: Introduction for economists and social scientists . 1st edition. Oldenburg, 2004.
- Engels: Basic knowledge of business intelligence . 1st edition. W3L, 2009.
- Holland, Scharnbacher: Fundamentals of statistics: data acquisition and presentation, dimensions, index numbers, time series analysis . 8th edition. Gabler, 2010.
Web links
Individual evidence
- ↑ jpowered.com , accessed 21 May 2011
- ↑ Dolic (2004); P. 85.
- ↑ technet.microsoft.com , accessed May 21, 2011 and technet.microsoft.com , accessed May 21, 2011.
- ↑ technet.microsoft.com , accessed May 21, 2011.
- ↑ web.zhaw.ch (PDF; 5.76 MB) ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. Retrieved May 21, 2011.
- ↑ sigop-sidops.ch (PDF; 384 kB) accessed on May 21, 2011; as well as wienerzeitung.at ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. Retrieved May 21, 2011.
- ↑ Bühner, Ziegler (2009); P. 68.
- ↑ Engels (2009); P. 111.
- ↑ Dolic (2004); P. 85.
- ↑ Dolic (2004); P. 87.
- ↑ Dolic (2004); P. 85.
- ↑ Presenting data in a pie chart. office.microsoft.com; Retrieved May 16, 2011
