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Introduction to Statistics: Help and Review9 chapters | 137 lessons

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Lesson Transcript

Instructor:
*Mia Primas*

Mia has taught math and science and has a Master's Degree in Secondary Teaching.

Dot plots are just one of the many methods used to organize statistical data. In this lesson, you will learn the definition of a dot plot, when it should be used, and how to create one.

As a school teacher, Mr. Page likes to have snacks available to reward his students for good behavior. He took a poll on the first day of school to find out what kinds of snacks the students prefer. This table shows the results for one of his classes:

Preferred Snack | Number of Students |
---|---|

Popcorn | 8 |

Pretzels | 4 |

M&M's | 5 |

Twizzlers | 6 |

Kit-Kats | 3 |

While the table was an efficient way to display the data, Mr. Page wanted to present it in a more visual format, so he decided to create a dot plot.

A **dot plot** is a graphical display used in statistics that uses dots to represent data. Dot plots can be used for **univariate** data; that is, data with only one variable that is being measured. Dot plots are useful when the variable is categorical or quantitative. **Categorical variables** are variables that can be organized into categories, like types of sports, ice cream flavors, and days of the week. **Quantitative variables**, on the other hand, are variables that can be measured and have numerical values. Population, shoe size, and heart rate are examples of quantitative variables.

Dot plots work very well for data with a small number of values. They would not work well for large sets of data, because a dot would need to be plotted for each value. Histograms or box plots are more useful for large sets of data.

To create a dot plot, we start by drawing a horizontal line with categories or numbers written beneath it. For the preferred snack results, Mr. Page wrote the names of each snack under the line. Then, he drew a dot above the line for each student who chose that particular snack. For example, he drew eight dots above popcorn, four dots above pretzels, five dots above M&M's, and so on. The numbers represent the **frequency** of each result, or how often the result occurs. Each dot represents one student, so the total number of dots is equal to the total number of students. In this example, there are 26 dots representing the snack choices for the 26 students.

The students in Mr. Page's class enjoyed seeing the results of the snack survey displayed on the board, so he decided to create another dot plot, showing the number of siblings for each student. His class was able to identify some interesting information, such as the range, shape, and mode of the data.

**Range** is the difference between the maximum and minimum values of a set of data. The values for number of siblings ranged from zero to four, so the range for this set of data is four. The **mode** is the value that appears most often in a set of data - this can quickly be identified in a dot plot by simply looking for the value that has the most dots. The mode for the sibling dot plot is one, because it has more dots than any of the other values.

The shape of a data distribution can be skewed left, skewed right, or normal. A normal distribution is shaped like a bell curve, with most of the values in the center. When the majority of the values are on the right, the data is skewed left, indicating that the data tapers off on the left end. On the other hand, if the data is mainly on the left end and tapers on the right, it is considered to be skewed right.

The sibling dot plot is skewed right, which lets us know that more of the students have zero to two siblings, and that very few have three or four siblings. This also tells us that the **mean**, or average, is in the zero to two range, allowing us to estimate the mean without having to calculate it.

Dot plots are a type of graphical display that can be used to show a data distribution. They are simple to create and provide useful information such as the range, shape, and mode of a set of data. They are used for univariate data when the variable is categorical or quantitative. Because individual dots must be drawn for each value in the data, dot plots are ideally used for small sets of data.

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Introduction to Statistics: Help and Review9 chapters | 137 lessons

- Descriptive & Inferential Statistics: Definition, Differences & Examples 5:11
- Difference between Populations & Samples in Statistics 3:24
- Defining the Difference between Parameters & Statistics 5:18
- Estimating a Parameter from Sample Data: Process & Examples 7:46
- What is Quantitative Data? - Definition & Examples 4:11
- What is Categorical Data? - Definition & Examples 5:25
- Discrete & Continuous Data: Definition & Examples 3:32
- Nominal, Ordinal, Interval & Ratio Measurements: Definition & Examples 8:29
- The Purpose of Statistical Models 10:20
- Experiments vs Observational Studies: Definition, Differences & Examples 6:21
- Random Selection & Random Allocation: Differences, Benefits & Examples 6:13
- Convenience Sampling in Statistics: Definition & Limitations 6:27
- How Randomized Experiments Are Designed 8:21
- Analyzing & Interpreting the Results of Randomized Experiments 4:46
- Confounding & Bias in Statistics: Definition & Examples 3:59
- Bias in Polls & Surveys: Definition, Common Sources & Examples 4:36
- Misleading Uses of Statistics 8:14
- Causation in Statistics: Definition & Examples 3:28
- Deductive Argument: Definition & Examples
- Dot Plot in Statistics: Definition, Method & Examples 3:57
- Skewness in Statistics: Definition, Formula & Example 6:49
- Uniform Distribution in Statistics: Definition & Examples 4:58
- Confidence Interval: Definition, Formula & Example 7:33
- Chi Square Distribution: Definition & Examples 4:55
- Chi Square Practice Problems 6:53
- Chi Square: Definition & Analysis 4:04
- How to Calculate a Chi Square: Formula & Example 4:13
- Go to Overview of Statistics: Help and Review

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