Help Manual

Contents






Sigma Magic Help Version 15

Box Plot

Overview

Box Plots are a great way to compare different sets of data on a single chart. Box Plots typically show the first quartile, median, and the third quartile with whiskers going out to the extreme values (min, max). If the min and max values are far away from the box, then the whiskers are truncated, and the extreme values are shown as stars (outliers). Box Plot can give us an idea of the central location and spread of the data points.

This tool can be added to your active workbook by clicking on Graph and then selecting Box Plot.

Inputs

Click on Analysis Setup to open the menu options for this tool.

Setup

A sample screenshot of the setup menu is shown below.
inputs
1
Chart Type: Specify the format of the chart. This selection is not enabled since there is only one format available.
2
Add Points: Specify if you want to display additional data points on the box plot. The available options are:
OptionDescription
NoneDo not show any additional data on the box plot.
Show MeanDisplay the mean value on the box plot. The mean value is shown using a small circle marker.
Show DataShow the individual data points on the box plot. Since data points may be overlapping, a small jitter value is added to the data points to spread them out.
3
Connector: Specify if the central value of the box plots need to be joined with a connector or a straight line. The default value is to not connect the mean values.
4
Outliers: Specify if you want to display the outliers on the box plot. Outliers are data that lies far away from the central values. The outliers are shown using a red star marker. The default option is to display the outliers.
5
Help Button: Click on this button to open the help file for this topic.
6
Cancel Button: Click on this button to discard any changes and close the dialog box.
7
OK Button: Click on this button to save any changes and compute the analysis outputs if possible.

Data

If you click on the Data button, you will see the following dialog box. Here you can specify the data required for this analysis. Data
1
Search Data: The available data displays all the columns of data that are available for analysis. You can use the search bar to filter this list and to speed up finding the right data to use for analysis. Enter a few characters in the search field and the software will filter and display the filtered data in the Available Data box.
2
Available Data: The available data box contains the list of data available for analysis. If your workbook does not have any data in tabular format, this box will display "No Data Found". The information displayed in this box includes the row number, whether the data is Numeric (N) or Text (T), and the name of the column variable. Note that the software displays data from all the tables in the current workbook. Even though data within the same table have unique column names, columns across different tables can have similar names. Hence, it is important that you not only specify the column name but also the table name.
3
Add or View Data: Click on this button either to add more data into your workbook for analysis or to view more details about the data listed in the available data box. When you click on this button, it opens up the Data Editor dialog box where you can import more data into your workbook, or you can switch from the list view to a table view to see the individual data values for each column.
4
Required Data: The code for the required data specifies what data can be specified for that box. An example code is N: 2-4. If the code starts with an N, then you will need to select only numeric columns. If the code starts with a T, then you can select both numeric and text columns. The numbers to the right of the colon specify the min-max values. For example, if the min-max values are 2-4, then you need to select a minimum of 2 columns of data and a maximum of 4 columns of data in this box. If the minimum value is 0, then no data is required to be specified for this box.
5
Select Button: Click on this button to select the data for analysis. Any data you select for the analysis is moved to the right. To select a column, click on the columns in the Available Databox to highlight them and then click on the Select Button. A second method to select the data is to double click on the columns in the list of Available Data. Finally, you can also drag and drop the columns you are interested in by holding down the select columns using your left mouse key and dragging and dropping them in one of the boxes on the right.
6
Selected Data: If the right amount of data columns has been specified, the list box header will be displayed in the black color. If sufficient data has not been specified, then the list box header will be displayed in the red color. Note that you can double-click on any of the columns in this box to remove them from the box.
7
View Selection: Click on this button to view the data you have specified for this analysis. The data can be viewed either in a tablular format or in a graphical summary.

Charts

If you click on the Charts button, you will see the following dialog box. Charts
1
Title: The system will automatically pick a title for your chart. However, if you would like to override that with your own title you can specify a title for your chart here. Note that this input is optional.
2
Sub Title: The system will automatically pick a subtitle for your chart. However, if you would like to override that with your own subtitle you can specify a subtitle for your chart here. Note that this input is optional.
3
X Label: The system will automatically pick a label for the x-axis. However, if you would like to override that with your own label for the x-axis you can specify a different label here. Note that this input is optional.
4
Y Label: The system will automatically pick a label for the y-axis. However, if you would like to override that with your own label for the y-axis you can specify a different label here. Note that this input is optional.
5
X Axis: The system will automatically pick a scale for the x-axis. However, if you would like to override that with your values for the x-axis, you can specify them here. The format for this input is to specify the minimum, increment, and maximum values separated by a semi-colon. For example, if you specify 10;20 then the minimum x-axis scale is set at 10 and the maximum x-axis scale is set at 20. If you specify 10;2;20, then, in addition to minimum and maximum values, the x-axis increment is set at 2. Note that this input is currently disabled and you will not be able to change this setting.
6
Y Axis: The system will automatically pick a scale for the y-axis. However, if you would like to override that with your values for the y-axis, you can specify them here. The format for this input is to specify the minimum, increment, and maximum values separated by a semi-colon. For example, if you specify 10;20 then the minimum y-axis scale is set at 10 and the maximum y-axis scale is set at 20. If you specify 10;2;20, then, in addition to minimum and maximum values, the y-axis increment is set at 2. Note that this input is optional.
7
Horizontal Lines: If you want to add a few extra horizontal reference lines on top of your chart you can specify the values here. The format for this input is numeric values separated by semi-colon. For example, if you specify 12;15 then two horizontal lines are plotted at Y = 12 and Y = 15 respectively. Note that this input is optional.
8
Vertical Lines: If you want to add a few extra vertical reference lines on top of your chart you can specify the values here. The format for this input is numeric values separated by semi-colon. For example, if you specify 2;5 then two vertical lines are plotted at X = 2 and X = 5 respectively. Note that this input is optional.

Verify

If you click on the Verify button, the software will perform some checks on the data you have entered. A sample screenshot of the dialog box is shown in the figure below. Verify The objective of this analysis as well as any checks that are performed is listed in this dialog box. For example, the software may check if you have correctly specified the input options and entered the required data on the worksheet. The results of the analysis checks are listed on the right. If the checks are passed, then they are shown as a green-colored checkmark. If the verification checks fail, then they are shown as a red-colored cross. If the verification checks result in a warning, they are shown in the orange color exclamation mark and finally, any checks that are required to be performed by the user are shown as blue info icons.

Outputs

Click on Compute Outputs to update the output calculations. Box Plot Example
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Notes: The text output of the analysis is sent to the Notes section. This section contains the summary of the inputs: the number of data points, any skipped rows, the number of groups, and whether means should be displayed on the box plot. Next, it contains the analysis results. The analysis results contain the following information for each group: group name, number of data points in that group, the mean value, median value, minimum and maximum values, and the quartiles (first quartile, third quartile, and the inter-quartile range). Finally, the conclusion section lists if there were any outliers found in the data set.

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Graphs: The graph section contains the box plot of the given data set. You can compare different groups of data to see if the medians are relatively similar for each of the groups. You can compare the variation (width of the box) to determine if the variations are similar for each of the groups. You can also look at where the median is located within the box to get an idea of the distribution is symmetric or not. Any outliers in the data are shown by a *. The mean value of the group is shown by a small circle (the mean value display can be turned off by changing the mean display option in the Analysis Setup dialog box). The mean value can be different from the median value if there are significant outliers in the data.

Notes

Here are a few pointers regarding this analysis:
  • Sometimes the values for Sigma Magic may not match output from Excel since Excel uses an archaic method to calculate the median and quartiles. This method is not used in this package to calculate the values. The numbers reported by Sigma Magic will match other statistical software packages.
  • You can use the standard Excel functions to format the graph. However, note that if you click on Compute Outputs again you may lose all the formatting that you have done to your graph.

Examples

Following examples can be found in the Examples folder.
  • Create a box plot for the data given in the data file. Determine if the data has any outliers (Order Entry Time.xlsm).
  • Create a box plot for the internet users age data. Determine if the data has any outliers (Internet Users Age.xlsm).
  • Create a box plot for the number of coupons used in a given city. Determine the median, quartiles and if the data has any outliers (Shopper Coupons.xlsm).