Pie chart
A pie chart (also cake or pie graph ) is a form of representation for fractional values of a whole as parts of a circle. The pie chart is circular and divided into several sectors of a circle, each circle sector thus represents a partial value and the circle the sum of the present values ( the whole). The alternative designation as a cake or a pie chart refers to sections of a round cake, which correspond to the circle sectors.
History
The first known use of pie charts can be found in William Playfair (1759-1823) publication 'The Statistical Breviary ' from the year 1801., The Scottish engineer and economist Playfair used this form of representation in his work to the territorial division of the Turkish Empire after to illustrate continents.
In the following time, this form of representation was initially received little attention. The French engineer Charles Joseph Minard in 1858, she reached up again to add a third dimension of information presentation. Since then, many variations of the pie chart were such as Polar, surface, radar, pie or 3D diagrams designed. The form most commonly used, however, is still the simple representation of a pie chart.
Properties and preparation
Pie charts are often used for representing distributions and proportions. The number of sub-values should be not more than 10; otherwise the chart is confusing. Several small part values are represented equally confusing. In this case, it is advisable to combine the values to a small portion of "Other " value. Usually increases the clarity if the partial values are sorted clockwise, the size and the majority value, like a clock, starts on the 12 - clock - line.
Pie charts can for example be create using a spreadsheet.
The circle sectors are each defined by radius lines from the edge to the center. The central angle between two adjacent radial lines determines the size of the circle sectors. The respective sector size ( in angle) is calculated as follows:
The radius of the circle is arbitrary; the calculated angles remain the same.
To better distinguish the respective sectors different colors, patterns and shades are used.
Outside the scientific operation, pie charts found in many external as well as internal presentations of companies. In addition, serving journalists of the pie chart to make proportions between groups, parties, parties concerned, or the like significantly, so also find pie charts repeatedly in newspapers and magazines again.
Variations
Exploded diagram of
Semi-circle diagram
Polar Area Chart
Donut chart
A special form of the classic pie chart is the donut chart. A donut chart displays value data as a percentage of the whole. Categories are represented by individual segments. Ring diagrams are generally used to represent percentages. While, in the circuit diagram, there is only the possibility of displaying a series of data, the ring can diagram two or more data lines illustrated and compared. The open area in the center of the diagram is often used to add a comment.
Exploded diagram of
In principle, the exploded representation of the structure of the graph is to be compared with the conventional display. However, a few slices are moved away a bit from the center, so that gaps are formed between the individual segments. This effect is used to draw attention to a specific part of the diagram. The exploded view is used both in the pie chart and the pie chart.
Semi-circle diagram
Semicircle charts are often used to visualize the distribution of seats in Parliament. Here, the semi-circle, the total number of seats represents the majority of the distribution can be read from the sectors. The representation of a semicircle is due to the usual allocation of Parties in the left-center- right scheme.
Polar Area Chart
This type of visualization is used for the representation of cyclically recurring phenomena. Attributed this chart type to Florence Nightingale. She presented in 1858 the relationship between deaths and hygiene conditions dar.
Criticism
The pie chart is not suitable for representing data of each scale levels. It is often used in the preparation of discrete data. Thus, it is especially recommended for the nominal and ordinal scale which, however, at interval and ratio scale makes little sense. This has the disadvantage of dimensionality. The user can display only one data series, ie a row or column, in a pie chart. If you want to compare two results, two pie charts to be created. Pie charts are with increasing number of characteristic values quickly become confusing. As a rule of thumb that a pie chart for more than seven forms is confusing. Good use is primarily as a comparison between two distributions in which the differences are very clear. However, it should be entirely dispensed with the representation of a distribution by a three-dimensional pie chart. The color design of the circular sectors may lead to distorting perception. Thus it can be emphasized unintentionally, for example, by a clumsy choice of color for individual segments, part of the distribution. In the eyes of the beholder a color- accented circle segment seems disproportionately large. The use of a pie chart should be considered only if only one data series to be displayed, no negative values occur, null values are not available and the categories represent parts of the whole pie chart.
Example
A department store manager wants to represent the distribution of purchases among the individual departments of the store in a pie chart. 32 Of the 95 Shopping acts attributable to the food section. The respective sector of the pie chart is calculated as follows:
The sector for sales in the food department must include 121.26 degrees. The calculation of the angular degrees for the other departments is shown in the table below.