Dot Plot Meaning
A dot plot, also known as a dot diagram, is a statistical chart consisting of data points on a relatively simple scale. Dot plots are considered as one of the easiest statistical plots, used for small data sets. Dot plots are used for highlighting clusters, gaps, skews in distribution, and outliers. When working with datasets larger than 20 or 30, it is better to use another statistical chart such as a histogram, as the dot plot will be less manageable.
Constructing a Dot Diagram
While constructing a dot diagram, data points are stacked in a column over a category. The height of the column denotes the frequency of observation in a given category. The categories of dot diagram given below are the numbers from 0 to 9, where 0, 1, and 5 occur three times, 2 occurs 7 times, 3 and 4 occurs six times, 6 occurs 4 times, 7 and 9 occurs 9 times, and 8 occurs two times.
The dot diagram given above represents the total number of data points and how the data points are distributed among certain categories.
Analyzing Dot Plot
A dot plot or dot diagram consists of a horizontal scale (a number line) on which dots are arranged to represent the numerical values of the data set. If the values in a data set repeat the dots are accumulated at that location. One dot is plotted for each repetition. We can say that dot diagrams represent the distribution of data.
Analyzing the dot plot of a given data set can be done easily in comparison to a long list of numbers. By looking at the dot plot diagram given below, you can see that dots are evenly spread with a peak at around 8 letters. The centre of the graph is between 6 and 7 letters. The dots are spread from 3 to 9 letters.
With a dot plot, you can easily count the number of times each category, or number is repeated. A dot plot is an optimum way of organizing numbers and values.
In a dot plot, you can easily count the number of times each category, or number is repeated. A dot plot is an optimum way of organizing numbers and values.
Dot Plot Interpretation
As you know, a dot plot is made up of dots plotted on a graph. Considering this, let us learn dot plot interpretation.
Each dot plotted in a dot graph denotes a specific number of observations from a given set of data (unless specified, assume that each dot represents one observation. If a dot represents more than one observation, that should be written on the plot.
The dots are arranged in a column over category, so that height of the column represents the absolute or relative frequency of observation in the category.
The pattern of data formed in a dot plot can be clearly stated in terms of symmetry and skewness only if the categories are quantitative, but if the categories are qualitative, a dot plot is not suitable to describe those terms.
In comparison to other types of graphs, dot plots are often used to plot frequency counts within a small number of categories, generally a small set of data.
Types of Dot Plot
There are two types of dot plot namely:
Wilkinson Dot Plot
Cleveland Dot Plot
Wilkinson Dot Plot
The Wilkinson Dot Plot represents the distribution of continuous data points, like a histogram. For example, the tempurature in a room throughout the day.
A histogram is shown in Wilkinson Dot Plot but represents the individual data points like P, Q, R, S shown below rather than bins. These points can consider any values like Mathematics marks of four friends, or the number of minutes taken by four kids to finish their lunch.
Cleveland Dot Plot
Cleveland dot plot is a good alternative to a simple bar chart, specifically if you have more than a few items.
It does not take much for a graph to look cluttered. In the same amount of space, many more values can be plotted in a dot plot and it is easier to read as well.
Although this type of dot plot is similar to a bar chart but uses location rather than the duration of the data encoding values.
Just like the height of the bar chart represents the number of items, the position of dots in the graph represents the number of items for that category or bin.
For example, the Cleveland dot plot given below represents the trend in literacy rate in Post independent India.
For example,
Dot Plot Examples
1. The dot plot given below represents the number and types of pizzas ordered for the party. By analyzing the dot plot, determine the number of pizzas ordered for the party, How many of these pizzas were pepperoni or cheese?
Solution:
To determine the number of pizzas ordered for the party, add all of the data points together on a dot plot. In total, 22 pizzas were ordered for the party.
To find the numbers of pizzas ordered for a certain category, sum up all the points in those categories. There are 7 pepperoni pizzas and 5 cheese pizzas. In total 12 pizzas are of cheese or pepperoni.
2. The dot plot given below represents the height of each kid at Mr. George's daycare. Each dot represents the height of different kids. Determine the height of the shortest kid.
Solution:
The height range of kids on the axis is from 83 - 86.
The 3 dots are plotted on bin - 83 which implies that there are 3 kids whose height is 83.
Therefore, the height of the shortest kid is 83.
FAQs on Dot Plot
1. What is a dot plot in statistics?
A dot plot is a simple statistical chart that displays data using dots above a number line. Each dot represents a single data point. It is used to visualise the frequency and distribution of a small dataset, making it easy to see patterns like clusters, gaps, and outliers.
2. How do you construct a dot plot step-by-step?
To construct a dot plot, you can follow these simple steps as per the standard method:
- Step 1: Draw a horizontal line, which will serve as your axis.
- Step 2: Label the axis with the range of values from your dataset. Ensure the scale is consistent.
- Step 3: For each data point in your set, place a dot above its corresponding value on the axis.
- Step 4: If a value repeats, stack the dots vertically. The height of the stack shows the frequency of that value.
3. What are the main components of a dot plot?
A dot plot consists of a few key components that work together to represent data clearly:
- A horizontal axis: This is essentially a number line that is scaled to include all the values in the dataset.
- Dots: Each dot represents a single observation or data point.
- Frequency: The number of dots stacked above a specific value on the axis indicates the frequency of that value in the dataset.
4. What are the two main types of dot plots explained in statistics?
There are two primary types of dot plots, each with a slightly different application:
- Wilkinson Dot Plot: This type is used to represent the distribution of continuous data, similar to a histogram, but it shows individual data points instead of grouping them into bins.
- Cleveland Dot Plot: This type is an alternative to a bar chart and is effective for displaying more categories without looking cluttered. It uses the position of the dot to represent value, rather than the length of a bar.
5. How do you interpret the shape of a dot plot distribution?
Interpreting a dot plot involves observing how the dots are spread across the axis. You should look for key features such as:
- Clusters: Areas where many dots are grouped together, indicating common values.
- Gaps: Empty sections on the axis where no data points fall.
- Outliers: Dots that are located far away from the main group of data.
- Symmetry and Skewness: You can assess whether the data is spread evenly (symmetrical) or if it trails off to one side (skewed).
6. In what situations is a dot plot more useful than a histogram?
A dot plot is more useful than a histogram for small datasets (typically under 30 data points). The primary advantage is that a dot plot retains individual data values, allowing you to see every single point. In contrast, a histogram groups data into bins, causing the identity of individual observations to be lost. Therefore, for detailed analysis of a small set of numbers, a dot plot is often preferred.
7. What is the key difference between a dot plot and a scatter plot?
The key difference lies in the number of variables they display. A dot plot is used to visualise the distribution of a single quantitative variable. A scatter plot, on the other hand, is used to show the relationship between two different quantitative variables, with one plotted on the x-axis and the other on the y-axis.
8. Can a dot plot be used for categorical data? Provide an example.
Yes, a dot plot can be effectively used for categorical data, especially when you want to show the frequency of each category. For example, you could create a dot plot to show how many students chose different fruits as their favourite. The horizontal axis would list the fruit names (Apple, Banana, Orange), and dots would be stacked above each name to show how many students chose that fruit.
