Help Manual

Contents






Sigma Magic Help Version 15

Histogram

Overview

Histograms can be used to compare different sets of data. Histograms are similar to Dot Plots except that data points are displayed in groups rather than separately as individual data points. If you have less than 50 data points, it may be better to use Dot Plots instead of Histograms. Histograms can help visualize which data values occur the most often and give us an idea of the minimum and maximum values and help determine the nature of the distribution of the data.

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

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
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Data Type: Specify the type of data for this analysis.
OptionDescription
ContinuousUse this option for continuous data. Continuous data can have almost any numeric value and can be meaningfully subdivided into finer and finer increments, depending upon the precision of the measurement system.
DiscreteUse this option is your data is discrete. Discrete data contains finite values - for example, binary, categorical data.
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Fit Distribution: Specify if you want to fit a distribution to your histogram.
OptionDescription
NoneDo not fit any distribution to the histogram.
Distribution NameFit the selected distribution to the histogram. The default is to fit a Normal distribution to the selected data.
3
Help Button: Click on this button to open the help file for this topic.
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Cancel Button: Click on this button to discard any changes and close the dialog box.
5
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
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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.
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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.
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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.
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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.
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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.
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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.
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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.

Bins

If you click on the Charts button, you will see the following dialog box. Charts
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Bin Algorithm: Specify the algorithm to use the bin sizes for the histogram. The shape of the histograms are very sensitive to the number of bins and it is important that you correctly determine the right number of bins to use for your graph.
OptionDescription
Auto The software will determine the most appropriate bin size to use for this chart.
Freedman-DiaconisThe software will determine the bin-width based on the Freedman-Diaconis algorithm. You can override the min and max values if required.
ManualSpecify the minimum, maximum, and the bin width. Here you have maximum control of the settings to plot the histogram. The number of bins is auto calculated based on the values you enter.
Shimazaki-ShinomotoThe software will determine the bin-width based on the Shimazaki-Shinomoto algorithm. You can override the min and max values if required.
Square RootThe software will determine the bin-width based on the Square Root algorithm. You can override the min and max values if required.
SturgesThe software will determine the bin-width based on the Sturges algorithm. You can override the min and max values if required.
Terrell-ScottThe software will determine the bin-width based on the Terrell-Scott algorithm. You can override the min and max values if required.
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Bin Width: Specify the width of each bin. This can only be specified if the Bin Algorithm is set to Manual, otherwise it is automatically determined for you.
3
Min Value: Specify the minimum value for the histogram.
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Max Value: Specify the maximum value for the histogram.

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.
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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.
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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.
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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.
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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.
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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. A sample screenshot of the worksheet is shown below. outputs
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Notes: The text output of the analysis contains a summary of the inputs - specifically the type of data (continuous or discrete), the type of fit to display on the histogram, whether the bins are calculated automatically or manually. If the bins are calculated manually, the parameters to determine the bins are also listed in this section. The analysis results contain for each group, the name of the group, the mean and median values, the min and max values, the first and third quartiles, interquartile range, the range and standard deviation of the data points.

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Graphs: The graph section shows a plot of the histogram for each group along with a superimposed curve fit. You can compare different groups of data to see if the Histograms are relatively similar for each of the groups. If a curve fit is superimposed on the histogram, then you can compare the histogram to the curve fit to see if there is a close match between the two.

Notes

Here are a few pointers regarding this analysis:
  • Since we are using multiple axes for plotting the Histograms. If you just change one of the axes then your Histogram may not appear properly on the graph. You will have to proportionately scale both the axes of the Histogram if you desire to change the axes limits.

Examples

Following examples can be found in the Examples folder.
  • Create a histogram for the strength of a component provided by 2 suppliers (Company Weekly Revenue.xlsm)
  • Create a histogram for the revenue generated by a company (Company Weekly Revenue.xlsm)
  • Create a histogram for the unemployment rate of a developed nation collected from 1980 to 2013. Is the data normally distributed? What conclusions can you draw from this data set? (Unemployment Rate.xlsm)
  • Create a histogram of the city high temperatures - Refer to Q1 on problems tab. What conclusions can you draw from this data? (City Weather.xlsm)