Help Manual

Contents






Sigma Magic Help Version 17

Box Plot

Overview

Box Plots are a great way to compare different data sets on a single chart. Box Plots typically show the first, second, and third quartile with whiskers going out to the extreme values (min, max). If the min and max values are far from the box, 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 overlap, 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 needs to be joined with a connector or a straight line. The default value is not to connect the mean values.
4
Outliers: Specify if you want to display the outliers on the box plot. Outliers are data that lie 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: If possible, click this button to save any changes and compute the analysis outputs.

Data

You will see the following dialog box if you click the Data button. 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 speed up the search for the right data 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 has no 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 crucial that you not only specify the column name but also the table name.
3
Add or View Data: Click on this button to add more data to your workbook for analysis or to view more details about the data listed in the available data box. This button opens the Data Editor dialog box, where you can import more data into your workbook. You can also 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, select only numeric columns. You can choose numeric and text columns if the code begins with a T. The numbers to the right of the colon specify the min-max values. For example, if the min-max values are 2-4, you must select a minimum of 2 columns of data and a maximum of 4 columns 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 choose 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 choose the data is to double-click on the columns in the list of Available Data. Finally, you can 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: The list box header will be black if the right number of data columns is specified. If sufficient data has not been specified, then the list box header will be displayed in red color. Note that you can double-click on any of the columns in this box to remove them from the box.
6a
Analysis Variables: This list box contains the data used to create the plot. This list box is mandatory; at least one column must be specified. Note that the values specified in this column must be numeric. If multiple columns are specified, the box plot is created using the data in each column.
6b
Categorical Variables: This list box contains the categories to use to create the box plot. This list box is not mandatory. This list box can contain either numeric or text data. Note that we can specify up to two categories. If data has been selected for this list box, then the groups specified here are used to split the analysis variables into multiple data sets, and a box plot is created for each group. All the groups identified here will be plotted on the same chart.
6c
By Variable: This list box contains the categories to use to create the box plot. It is not mandatory and can contain either numeric or text data. Note that we can specify up to one column here. If data has been selected for this list box, then the groups specified here are used to split the analysis variables into multiple data sets, and a box plot is created for each group. All the groups identified here will be plotted on separate charts.
7
View Selection: Click on this button to view the data you have specified for this analysis. The data can be viewed in a tabular format or a graphical summary.

Charts

You will see the following dialog box if you click the Charts button. Charts
1
Title: The system will automatically pick a title for your chart. However, if you want to override that with your 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 want to override that with your subtitle, 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 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 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 determine the minimum, increment, and maximum values separated by a semi-colon. For example, if you specify 10;20, 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 cannot 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 determine the minimum, increment, and maximum values separated by a semi-colon. For example, if you specify 10;20, the minimum y-axis scale is set at 10, and the maximum y-axis 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: You can specify the values here to add a few horizontal reference lines to your chart. The format for this input is numeric values separated by semi-colon. For example, if you specify 12;15, two horizontal lines are plotted at Y = 12 and Y = 15, respectively. Note that this input is optional.
8
Vertical Lines: You can specify the values here to add a few extra vertical reference lines to your chart. The format for this input is numeric values separated by semi-colon. For example, if you specify 2;5, two vertical lines are plotted at X = 2 and X = 5, respectively. Note that this input is optional.

Verify

If you click the Verify button, the software will perform some checks on the data you entered. A sample screenshot of the dialog box is shown in the figure below. Verify The software checks 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, they are shown as green-colored checkmarks. If the verification checks fail, they are shown as a red-colored cross. The verification checks are shown in the orange exclamation mark if the verification checks result in a warning. Finally, any checks required to be performed by the user are shown as blue info icons.
1
Item: The left-hand side shows the major tabs and the items checked within each section
2
Status: The right-hand side shows the status of the checks.
3
Overall Status: The overall status of all the checks for the given analysis is shown here. The overall status check shows a green thumps-up sign if everything is okay and a red thumps-down sign if any checks have not passed. Note that you cannot proceed with generating analysis results for some analyses if the overall status is not okay.

Outputs

Click on Compute Outputs to update the output calculations. Box Plot Example
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Notes: The analysis text output is sent to the Notes section. This section summarizes 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 data groups to see if the medians are relatively similar for each group. You can compare the variation (width of the box) to determine if the variations are identical for each group. You can also look at where the median is located within the box to understand whether the distribution is symmetric. Any outliers in the data are shown by a *. The mean value of the group is indicated 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 differ from the median value if the data has significant outliers.

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 format the graph using the standard Excel functions. However, note that if you click on Compute Outputs again, you may lose all the formatting you have done for your graph.

Examples

The following examples are in the Examples folder.
  • Create a box plot for the data in the data file. Determine if the data has any outliers (Order Entry Time.xlsx).
  • Create a box plot for the internet users' age data. Determine if the data has any outliers (Internet Users Age.xlsx).
  • 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.xlsx).