2.2.4. Charts with lines

Line chart (or Line graph)

Definition: "Graphical device that displays quantitative information or illustrates relationships between two changing quantities (variables) with a line or curve that connects a series of successive data points." (BusinessDictionary.com, n.d.).

An example is shown in Figure 13.


Figure 13. Example of a line chart.
One of the two variables is often time (in months, years, etc.). The line charts are often used to show a trend.

Frequency polygon

Definition: "A distribution of discrete variates may be represented graphically by plotting the points, and drawing a broken line through them." (Kenney, 1939).

An example is shown in Figure 14.

Figure 14. Example of a polygon.
The definition by Kenney mentions the frequency polygon is used for discrete variates. However the frequency polygon is often used for grouped tables.

Ogive

Definition: "The graphs of cumulative frequencies" (Kenney, 1939).

An example is shown in Figure 15.


Figure 15. Example of an ogive.

Pareto diagram/plot

According to some authors a Pareto diagram is any diagram with the bars in order of size (Joiner, 1995; WhatIs.com, n.d.), while others suggest that a line representing the cumulative relative frequencies should also be included (Weisstein, n.d.).

In below are two examples. The first example (Figure 16) uses one vertical axis, the second (Figure 17) uses two.


Figure 16. Example of a Pareto diagram with one vertical axis.

Figure 17. Example of a Pareto diagram with two vertical axis.

Pareto (1919) described that in Italy 80% of the land was owned by 20% of the population. He noticed similar divisions in other countries. It is unclear who the first was to name the diagram after him.

>>Next section: Using technology to create diagrams

References
BusinessDictionary.com. (n.d.). What is line graph? definition and meaning. Retrieved April 20, 2014, from http://www.businessdictionary.com/definition/line-graph.html
Joiner. (1995). Pareto charts: plain & simple. Madison, Wisc.: Joiner Associates.
Kenney, J. F. (1939). Mathematics of Statistics; Part one. London: Chapman & Hall. Retrieved from http://archive.org/details/MathematicsOfStatisticsPartI
Pareto, V. (1919). Manuale di economia politica: con una introduzione alla scienza sociale. Milano: Societa Editrice Libraria. Retrieved from http://archive.org/details/manualedieconomi00pareuoft
Weisstein, E. W. (n.d.). Mode from MathWorld. Text. Retrieved April 5, 2014, from http://mathworld.wolfram.com/Mode.html
WhatIs.com. (n.d.). What is Pareto chart (Pareto distribution diagram)? Retrieved April 20, 2014, from http://whatis.techtarget.com/definition/Pareto-chart-Pareto-distribution-diagram