2022 Introduction to Statistics in Research Mitchell 2nd ed

I N T R O T O R E S E A R C H : D A T A V I S U A L I Z A T I O N & C O M M O N S T A T T E S T S

Comparative Dot Plot

In a comparative dot plot, you use univariate, numerical data with observations from two or more groups. It is the same process as one dot plot, you are just comparing the two dot plots.

Example: Assume that another professor (Professor Skew) gave the same ten question quiz but scored it more leniently. Here is the student scores.

6

8

10

8

8

7

9

8

10

8

7

8

9

7

7

8

8

7

8

7

6

6

6

5

5

9

2

Table 86: Professor Skew's quiz scores for a ten-point quiz

Now compare the original dot chart to Professor Skew's dot chart

Original Dot Plot DOT PLOT 1

Dot Plot from Professor Skew's class DOT PLOT 2

Table 87: Original Dot plot for class 1 - Professor Fair

Table 88: Dot Plot from class 2 - Professor Skew

Is the distribution in Professor Skew's class symmetric?

No! In dot plot 2, the distribution has a longer tail on the left side. This distribution is negatively skewed. The direction of skewness is always in the direction of the longer tail.

What else do you notice?

1) The center of the distribution is larger in Dot Plot 2 (8 instead of 6).

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