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Dot Plots

Plotting is an important part of statistics as a pictorial representation of data gives a clear idea of data. Dot plots are a visualization of data which can give information about the frequency distribution of the data. A dot plot can give an overall view of the data based on if it is skewed or not. A dot plot can be termed as right skewed or left skewed if it has fewer observations towards right or left respectively.

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The graphical representation of data using dots is known as a dot plot. Each dot will be representing a number of observations from a data set. Dot plot will be formed on a line which represents the variable or categorical data. It does visually represents data in different intervals or discretely. It analyzes the frequency of data in a given data table. A dot plot will be called right skewed if it has a fewer observations on that side. It will be left skewed if it has fewer observation on the left side. An outlier to a dot plot is the observation different from rest of the observations.

Creating a Dot Plot

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To create a dot plot, first, a data set should be taken. Then, in the rectangular axes write the intervals or the names and corresponding to it give the number of dots.

In a discrete mathematics class, a survey has been done on twenty students about which author they prefer to choose for studying discrete. The authors given are Rosen, Chapra, and Usha. Out of twenty, ten prefer books written by Rosen, three prefer books written by Usha and seven prefer books by Chapra. To make a dot plot, One line will have three points representing the three authors. Corresponding to each author the number of dots will be plotted.

How to Read Dot Plots

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If a dot plot has been given, then corresponding to each variable dots will be plotted. To know the frequency of a data in the given data set, we need to see the number of dots corresponding to the variable. For example, we have been given the following dot plot where each dot represents a subject.

How to read dot plots
The frequency table representing the dot plot is given here.

 Grades Number of subjects
 A+  1
 A  2
 B+  2

 The given plot can be called left-skewed. The skewness and symmetry can be told only for the data which is quantitative, not qualitative.


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Example 1: From the give dot plot where a number of dots represent a number of persons getting the respective color bands, draw the data in a tabular form.

Examples on Dot Plots

Solution: The given table shows the dot plot in a tabular form.

Number of persons
 Red  5
 Blue  6
 Green  2
Example 2: Tell about the behavior of data from the given dot plot.

a. Left-skewed
b. Right, skewed
c. Symmetric

Solution: As the data is having less number of observations on the right side, hence the data cal be called right skewed.
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