Table of contents
What is a Box Plot?
This article will provide box plot examples and detailed information on how you can make a box or whisker plot with labels in excel. Before we get started, let’s first answer the fundamental question “What is a box or whisker plot?”
Box plots allow you to visually compare the variation among the data sets. It also makes it easy to make comparisons in a quick manner. Box plots with labels are also used in statistics to visually display different parameters at once.
Graphical Analysis is a renowned way to analyze Six Sigma projects’ problems. It provides insight into data and is a great way to visualize data patterns. There are many graphic tools, such as Chart. Scatter Diagrams, Histograms and Pareto Chart show different characteristics of the data, such as the trend, frequency, dispersion, and shape of the distribution. Box plot, also known as Whisker plot, is a pictorial representation of continuous data. The box plot displays the Max, Min, and median values, as well as the interquartile range Q1, Q3, and outlier.
Rectangles can be used to show the second and third quartiles. A vertical line shows the Median value. On both sides of this rectangle, horizontal lines are drawn to indicate the lower and upper quartiles. Because the lines that extend vertically from the boxes give it its name box and whisker, These lines indicate the variability between the lower and upper quartiles.
- Median.
- Maximum.
- Minimum
- The first quartile (0-25%)
- Third quartile (75%)
Why box plots?
Box plots with labels can be very useful and simple to understand. It graphically shows the variation among multiple variables as well as the variations within each range.
This is also known as a box and whisker plot, or “five-number summary.” It includes quartiles and medians, as well as the highest and most important values. It illustrates how data from within these ranges can be used to aid in decision-making.
When should you use box plots?
- They’ll allow you to compare data sets from different sources and determine if they have any relationship
- You can compare the changes in the process before and after the improvements
- They allow you to quickly display different parameters
- To view the median, interquartile range, and outliers within the data set
- If the data are in metric scale levels such as temperature, age, etc.
What can box plots tell us?
- Middle values: The box indicates the range where the middle 50% of all data is located
- Median: The blue horizontal line indicates the median value of the group
- 1st Quartile, and 3rd Quartile: The box’s lower end corresponds to the 1st quartile, while the upper half corresponds to the 3rd quartile.
- It is useful in visualizing the spreads of
- Ex. Stock 1 typically has the least variation
- Skewness: If the box line is not centered, you can see if your data distribution is off
- Ex. Stock 4’s median is not centered, thus this data is skewed
- Extreme values: The vertical lines (whiskers), show the max and minimum values
- Ex. Stock 5 tends to have higher values
- Data that isn’t between whiskers should be plotted as outliers using dots, small circles and stars
- Box plots may also use an additional character to represent the mean of the sample data
- Cross-hatch is used on some whisker plots. All box plots will have whiskers
How to Create a Box and Whisker Plot?
Follow these steps:
- Collect the data: Collect the data you need to create plots
- This will help you organize the data. Sort them numerically, ascending or increasing
- Calculate Medians: Determine the Median for this data range. This Median divides the data into two halves. To find out the Medians for the two halves, calculate the Medians. The Median will have equal numbers on each side if the data set contains an odd number of numbers. If the data set contains even numbers, the Median would have the same number on both sides
- Calculate 1 first and 3 rd Quartiles: You can find the Median for each half by using the following formula
- Draw plot lines: Next, draw plot lines and mark Median and Quartiles
Box Plot Example
Example: Draw a box plot for the 15 following points:
23,28,44,72,66,54,89,91,26,24,59,74,81,36,77
Step 1: Organize data: Arrange data in ascending order
23,24,26,28,36,44,54,59,66,72,74,77,81,89,91
Step 2: Calculate the median 23 , 24 , 26 , 28 , 36 , 44 , 54 , 59 , 66 , 72 , 74 , 77 , 81 , 89 , 91
The median value is 59.
Step3: Locate 1 st Quartile. Find the median of half the data set.
23 , 24 , 26 ,28, 36 , 44 , 54
28 is the median value.
Step4: Locate 3 rd Quartiles: Find the median of the upper half of the data collection
66 , 72 , 74 ,77, 81 , 89 , 91
The median value is 77.
Step 5: Draw 5 numbers summary: Draw plot lines, mark the lowest, highest points, median, and quartiles.
Box and Whisker Plot
This plot can be used for many purposes. Below are some of its main advantages and features:
- It’s easy to use: This is a great way to visualize numerical data groups graphically, especially when using quartiles.
- No assumptions
- Skewness, dispersion, and skewness: Box plots are not parametric. The space between the different parts of the box shows how the data is distributed.
- Different statistical values: These plots can be used to estimate range, midrange, mid-hinge, and interquartile ranges. Standard deviations and trimean are also possible. These plots can be used to determine the Median, Maximum, and Minimum. They also help you find the 1st Quartile (25%), and 3rd Quartile (75%). You can find the Median, Median, 2nd, 9th, and 25th percentiles, as well as the Median.
- Uniformity: These plots have a uniform appearance. The first and third quartiles are located at the top and bottom of the box. The Median or second quartile is indicated by the bands within the box.
- Easy comparisons: This makes it easier to compare data sets between them.
- Equal spacing: If the data distribution is normal, then all marks on the plot should be equally spaced.
How to make box plots with excel
Excel allows you to easily present data in many formats including Box plots. Excel offers pivot tables, bar graphs and more. This makes it easier to present data in an easily understandable format.
To create your box plot with excel, follow the steps below from Statology:
Step 1: Enter your data.
Add the values of your dataset into one column:
Step 2: Calculate the five number summary
To create a box plot with labels, we typically need to know the median value for a dataset. However, we will use a candlestick to create something that looks similar to a box plot because excel does not have that option.
To create candlestick charts, we need to know the minimum, maximum, 1st, 2nd, and 3rd quartiles of each dataset. Below is a list of the formulae you can use to calculate these numbers.
Step 3: Create your box plot.
Now, highlight the values in the columns A through E in the first row:
Click the Insert tab along the top ribbon, then click Chart in the dropdown menu:
In the Chart Editor window that appears on the right side of the screen, click the dropdown menu for Chart type and then click the chart type titled Candlestick chart.
Once you’ve done that, you’ll see a chart like the one below:
This is how to interpret the chart:
- The top line is the maximum value of the data set ( 28).
- The value of the third quartile ( 22 ) is shown at the top of the box.
- The value of the first quarter ( 7.5), is shown at the bottom of the box
- The final line is the minimum value for the dataset ( 4).
