Help Manual

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Sigma Magic Help Version 17

Basic Statistics

Overview

The basic Statistics tool is used to calculate some basic statistical information about the data and plot a histogram of the given data. You can use this analysis whenever you have collected any data and want to summarize it.
MeasureData TypesDescription
Freq TableBinary, Nominal, OrdinalProvides a table of the frequencies of different categories present in the data.
MeanDiscrete, ContinuousReports the average or the mean value of the data within that group
MedianOrdinal, Discrete, ContinuousReports the median value of the data. The median value is the central value of the data when the data is put in either increasing or decreasing order. For ordinal data, we need the categories to be numeric to report the median value.
ModeAll TypesReports the most frequently occurring category for the binary, nominal, and ordinal data and the most frequently occurring data value for discrete and continuous data types within a group.
Trimmed MeanDiscrete, ContinuousReports the mean value after subtracting the bottom 5% and the top 5% of the data points. It is like reporting the mean value after possibly removing the outliers.
MinOrdinal, Discrete, ContinuousReports the minimum value observed in the data. Note that this value is reported only if the categories for the ordinal data type are numeric. No minimum values are reported if text values are entered in the category column.
MaxOrdinal, Discrete, ContinuousReports the maximum value observed in the data. Note that this value is reported only if the categories for the ordinal data type are numeric. No maximum values are reported if text values are entered in the category column.
RangeOrdinal, Discrete, ContinuousReports the range values (max-min) observed in the data. Note that this value is reported only if the categories for the ordinal data type are numeric. No range values are reported if text values are entered in the category column.
StdevDiscrete, ContinuousReports the sample standard deviation value for the given data set within a group. Note that this is the sample standard deviation and not the population standard deviation.
VarianceDiscrete, ContinuousReports the variance value, which is the square of the standard deviation for the given data within a group. Note that this is the variance of the sample and not the population.
Q1Ordinal, Discrete, ContinuousReports the first quartile of the data values for discrete and continuous. This value is reported for ordinal data only if the category values are numeric. The first quartile means that 25% of the data points are less than Q1, and 75% of the data points are greater than Q1.
Q3Ordinal, Discrete, ContinuousReports the third quartile of the data values for discrete and continuous. This value is reported for ordinal data only if the category values are numeric. The third quartile means that 75% of the data points are less than Q3, and 25% of the data points are greater than Q3.
IQROrdinal, Discrete, ContinuousReports the difference between Q3 and Q1 values. This value is reported for ordinal data only if the category values are numeric.
SumDiscrete, ContinuousReports the sum of all the data values within a group.
SSQDiscrete, ContinuousReports the sum of squares of all the data values within a group. Note that the mean value is not subtracted from the data to calculate the Sum of Squares values.
CVDiscrete, ContinuousReports the coefficient of variation for the given set of data within a group. The coefficient of variation is the ratio of the standard deviation to the mean value. It reports the amount of variation in the data. If CV < 1, we can consider the data as having low variation; if CV > 1, then the data has high variation.
SkewnessContinuousReports a measure of the Skewness of the data. This measure can be used to check if the distribution is symmetric. If skewness is 0, then the distribution is symmetric. If the skewness is negative, the left tail is longer; if the skewness is positive, the right tail is longer.
KurtosisContinuousReports a measure of the shape of the distribution. If the Kurtosis is close to 3, the shape of the distribution is similar to the normal distribution. If Kurtosis is less than 3, there are fewer outliers; if Kurtosis is greater than 3, there could be more outliers.
NormalityContinuousReports the P value of the normality test to check if the given data is normally distributed. If the P value is less than alpha, we conclude that the data is not normally distributed.
CIContinuousReports the confidence interval of the mean value. The confidence interval reports the likelihood of where the population mean is expected to lie and is based on the variation in the data and the confidence level required in the analysis.


This tool can be added to your active workbook by clicking on Stats and then selecting Basic Stats under the Tool Wizard menu.

Analysis Setup

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

Setup

A sample screenshot of the setup menu is shown below.
inputs page 1
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Data Type: Click on the data type to specify the type of input data. The statistics you can compute and the graphs you can display depend on your data type. Following are the available data types for this option:
OptionDescription
Binary Binary data has two possible values (like Good/Bad or True/False or 0/1).
NominalNominal data has more than two categories, but they cannot be ranked (like nationality, religion, etc.).
OrdinalOrdinal data has more than two categories, and they can be compared with each other and ranked (like the grades in an exam A > B > C).
DiscreteDiscrete data is like count data that has only a finite set of values (like the number of defects in a product example 20, 30, 43).
ContinuousContinuous data can take any arbitrary value (like the temperature of the room example, 34.53 degrees centigrade).
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Notes Type: Specify the type of notes you would like to generate from this analysis. The available options are:
OptionDescription
AutoThe system will automatically pick multiple columns.
Single ColumnSpecify if you want the descriptive stats in a single column for each group. Use this option if you have a large number of groups.
Multiple ColumnsSpecify if you want to display the descriptive stats for all groups in a column format. Use this option if there are fewer groups for ease of comparison.
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Statistics: To select the statistics you want to display for each analysis, select the appropriate checkbox next to the statistic you are interested in. Depending on your data type, only those metrics that are suitable for that data type can be selected. For example, you cannot calculate the mean value for binary data. You can select a set of metrics for ordinal data to calculate only if the categories are numeric. For example, if you are measuring the survey responses on a Likert scale with Disagree, Neutral, or Agree. You can't calculate the median value if you enter these as categories. Still, if you transpose the data to numeric values (1, 2, 3), you can report the statistics, such as the median. For discrete and continuous data, the data column must be numeric.
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Help Button: Click on this button to open the help file.
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Cancel Button: You can click on this button to cancel any changes you have made in the Analysis Setup and exit this form. No outputs are computed or updated.
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OK Button: You can click on this button to save any changes you have made in the Analysis Setup and recompute all the outputs (notes and graphs section). Note that the outputs are updated only if you have all the required data entered on the worksheet. If there are missing inputs, you must enter the missing information and click on Compute Outputs to generate the analysis results.

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
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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 quickly find 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.
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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.
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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.
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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, 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.
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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.
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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.

The data you specify for this analysis depends on the options in the Setup tab.
OptionDescription
1If you want to analyze a single column of data, you can specify that column under Analysis Variables and leave the Grouping Variable blank.
2If you want to analyze multiple columns of data, you can specify the multiple columns under Analysis Variables and leave the Grouping Variable blank.
3If you are working with grouped data, then you enter the variable data under the Analysis Variables and the column that contains grouping information under Grouping Variables. Note that you can have up to two grouping variables.
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Analysis Variables: Specify the columns for which you want to determine the basic statistics. This column is numeric. You need to specify at least one column and can specify up to 100 columns.
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Grouping Variables: Specify the columns which contain the grouping information for the analysis variables. This column is optional, but if you specify a column, it should contain the same number of rows of data as the analysis variables. This column can be text or numeric. You can specify up to 2 columns for the grouping variables. All the groups are analyzed together.
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By Variable: Specify the columns that contain the grouping information for the analysis variables. This column is optional, but if you specify a column, it should include the same number of rows of data as the analysis variables. This column can be text or numeric. You can specify up to 1 column for the grouping variables. Note that if this column is selected, the analysis variables are split into multiple groups, and each group is analyzed separately.
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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
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Select Charts: Specify which charts you want to plot for your analysis. The available options are:
OptionDescription
HistogramPlot the histogram of the given data. This option is available for continuous and discrete data.
Box PlotPlot the box plot of the given data. This option is available for continuous and discrete data.
Time SeriesCreate a time series plot of the given data. This option is available for continuous and discrete data.
Bar ChartCreate a bar chart of the categorical data. This option is available for nominal and ordinal data.
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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.
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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.
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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.
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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 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, 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.
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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 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.
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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, 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: 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.
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Item: The left-hand side shows the major tabs and the items checked within each section
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Status: The right-hand side shows the status of the checks.
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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

A sample screenshot of the worksheet is shown below. This worksheet was created for continuous data with groups. Basic Stats Example
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Notes: The notes section summarizes the inputs, specifically the number of rows of data, any skipped rows, and the number of distinct groups. In the analysis results area, the analysis lists the measures you have selected to report, such as mean, median, minimum and maximum values, Q1, Q3, IQR, etc.
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Graphs: A bar chart of the data is shown for binary, nominal, and ordinal data. The graphical output box shows a histogram for discrete and continuous data. A normal curve is superimposed on the histogram.

Interpreting Results

The summary statistics for each group (Shift 1 and Shift 2) are shown in the notes section. We can see that the mean and median values are close for both shifts; however, the variation is slightly higher for Shift 1 than for Shift 2. There are only about 20 data points for both groups. The histogram shows that the data roughly follows the normal distribution. There are no outliers present in the data sets.

Notes

Here are a few pointers regarding this analysis:
  • If you are copying data from another Excel spreadsheet, ensure you do not copy any extraneous information, such as formatting. Ensure you always use "Paste Special" and only paste "Values" and nothing else. This will preserve the formatting on the worksheet.
  • The histogram is auto-created. You cannot change how the bin sizes are calculated in this tool. You must use the tool if you want more control over creating the histogram.
  • If you are calculating statistics for ordinal data such as min, max, range, quartiles, etc., you must enter numeric values for the categories. Otherwise, the software will be unable to compare them and rank them against each other.
  • You can change the number of decimal places displayed for the statistics by clicking on Options > General > Number Format.
  • When you change the data type, the column names will change only if no data is entered on the worksheet. The column names will not be altered once you enter the data on the worksheet and change the data type.

Examples

The following examples can be found by clicking the Examples button on the main menu bar.
  • Compute the mean, median, and IQR for the Pizza delivery time given in the data file (Basic Stats 1.xlsx).

Additional Info

Here are a few related topics of interest.