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Sigma Magic Help Version 17

Interval Plot

Overview

An Interval Plot tool can create an interval plot graph for a given set of data points. Interval Plots are a great way to compare different data sets on a single chart. Interval Plots show the mean value and the 95% confidence interval for the mean. These are very similar to a box plot but only show the central tendency and variation in the mean value, not the medians and quartiles as in a box plot.

This tool can be added to your active workbook by clicking on Graph and then selecting Interval 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
Plot Orientation: Specify the orientation of the individual value plot.
OptionDescription
HorizontalPlot a horizontal individual value plot.
VerticalPlot a vertical individual value plot.
3
Add Points: Specify if you want to display additional data points on the interval plot. The available options are:
OptionDescription
NoneDo not show any additional data on the plot.
Show MeanDisplay the mean value on the plot. The mean value is shown using a small circle marker.
4
Connector: Specify if the central value of the interval plots needs to be joined with a connector or a straight line. The default value is not to connect the mean values.
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, you must specify the column name and 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. When you click on this button, it 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, you must select only numeric columns. If the code begins with a T, you can select 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, 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 displayed in 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 interval 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, then the interval plot is created using the data in each column.
6b
Categorical Variables: This list box contains the categories to use to create the interval plot. It is not mandatory and can contain either numeric or text data. Note that we can specify up to two categories. Suppose data has been selected for this list box. In that case, the groups specified here are used to split the analysis variables into multiple data sets, and an interval 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 interval plot. It is not mandatory and can contain either numeric or text data. Note that we can specify up to one column here. Suppose data has been selected for this list box. In that case, the groups specified here are used to split the analysis variables into multiple data sets, and an interval 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 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 specify 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 specify 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 if you want to add a few extra horizontal reference lines on top of 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 if you want to add a few extra vertical reference lines on top of 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. If the verification checks result in a warning, they are shown in the orange exclamation mark, and finally, any checks that are 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. A sample screenshot of the worksheet is shown below. outputs
>
Notes: The text output of the analysis contains a summary of the inputs - specifically the number of data rows, groups, and the confidence interval. The analysis results consist of the mean, standard deviation, and the standard error of the mean value. It also shows the confidence bounds for the mean value.
>
Graphs: You can compare different groups, and if they have overlapping confidence intervals, we can conclude that the means are similar. We can conclude that the means differ if the confidence intervals do not overlap. The default value of the confidence level is 95%. If you want to change the value of the confidence level, you can change that using the Options button.

Notes

Here are a few pointers regarding this analysis:
  • 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 to your graph.

Examples

The following examples are in the Examples folder.
  • Create an interval plot for the data in the data file. Determine if the data has any outliers (Interval Plot 1.xlsx).



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