A dot plot, also referred to as a line plot, is a type of graph that shows the frequency with which a given object/event occurs in a set of data (as dots over a number line). They provide a relatively quick and simple way to organize and display small sets of data. It is similar to bar graphs in that the dots (like the height of a bar graph) represent the number of items in a particular category. Below is a dot plot showing the distribution of scores (0-10) of 20 students on a quiz.
Each of the yellow dots in the figure represents 1 of the 20 students. It tells us that 5 students scored a 10 on the quiz, 2 scored a 9, 4 scored an 8, and so on. This data can be used to determine things such as whether the quiz was fair or not. For example, if every student scored between a 0-2, it is likely that the quiz was too difficult. On the other hand, if all students scored 9s or 10s on the quiz, the quiz may have been too easy, or the students have a great grasp of the material.
Line plots (dot plots) vs line graphs
Dot plots are also referred to as line plots, which can cause some confusion with line graphs. Line plots and line graphs, despite the similar name, are not the same thing. They both represent data, but in different ways.
Line plots are used to display frequency data, while line graphs are more typically used to show how one variable changes relative to another. For example, a line plot may be used to show a distribution of temperatures over a year. A line graph, on the other hand, could show the average temperature over the course of the year. In regions that have four seasons, the line graph would show cooler weather in the fall and winter months, and warmer weather in the spring and summer months.
While the line graph shows us general patterns about the weather throughout the year, the line plot could instead give us an idea of how often the temperature fell below 32°F, exceeded 100°F, or tell us the most common temperature (mode) throughout the year in a specific region.
On top of generally displaying different types of data, line graphs can also more easily display larger quantities of data. In the example above, regardless how the line plot is structured, it would be difficult to display the temperature data over the course of a year in a clear way. Another type of chart, a frequency table, could display the data more effectively.