Help Manual

Contents






Sigma Magic Help Version 17

Sample Data

Overview

This tool can be used to sample data from a population. For example, if you have a large population and would like to select a subset of data for random analysis, you can specify the method to sample the data from this population. The population data is stored in the input column, and the sample data is stored in the output column.

This tool can be added to your active workbook by clicking on Stats and then selecting Random Numbers > Sample from Column.

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
Data Type: Specify the type of data you would like to generate. The data type determines the appropriate metrics to display in the output results. The available options are:
OptionDescription
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).
2
Num Samples: Specify the number of samples you would like to sample from the population. This number should be less than the total number of data points in the population.
3
Sampling Method: Specify the sampling algorithm to be used to generate the random numbers. The available options are:
OptionDescription
RandomA simple random sample will be used to sample the data.
SequentialThe data points are sampled sequentially from the population depending on the number of samples required - for example, every Nth data point is sampled. However, the starting value of the sample will depend on your random number generator with a given seed value.
StratifiedHere, you will need to enter both the group data and the population data on the worksheet. The group data is used to stratify the population so that the right percentage of data points can be sampled from each group. Within each group, the numbers are randomly selected.
ClusterHere, you will need to enter both the cluster information and the population data on the worksheet. The clusters are randomly selected based on the random number generator until the desired number of samples is obtained.
4
Random Seed: Specify the initial value for the random number algorithm. If the seed value is 0, different random numbers are generated each time. If you want the same set of random numbers to be generated, enter a positive integer value for the seed.
5
Help Button: Click on this button to open the help file for this topic.
6
Cancel Button: Click on this button to cancel all changes to the settings and exit this dialog box.
7
OK Button: Click on this button to save all changes and compute the outputs for this analysis.

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 finding 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. 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.
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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, 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.
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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 displayed in black if the right number of data columns is specified. If sufficient data has yet to be 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
1For random and sequential sampling, specify the column containing population data that you want to sample from under Population Variable. The Grouping Variable is not required and hence is disabled.
2For stratified sampling, specify the column containing population data that you want to sample from under Population Variable and the column containing group information under Grouping Variable.
3For stratified sampling, specify the column containing population data that you want to sample from under Population Variable and the column containing cluster information under Grouping Variable.
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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
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.
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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 currently disabled, and you cannot change this setting.
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-colons. 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 currently disabled, and you cannot change this setting.
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 currently disabled, and you will not be able to change this setting.

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. 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
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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

Click on Compute Outputs to update the output calculations. A sample screenshot of the worksheet is shown below. outputs The notes section contains the input summary - specifically the data type, the method used for sampling, the number of sample data, and the random seed. The analysis results vary depending on whether you have selected continuous or discrete for your data set. For the continuous data set, the analysis results show the number of data points and mean, median, minimum, maximum, and standard deviation values for both the population and the sample. Only the number of data points is displayed for a discrete data set.

The graphs section contains a 2D pictorial representation of the population data points in blue and the sampled data in red. This gives a visual indication of where the sample is located within the population.

Notes

Here are a few pointers regarding this analysis:
  • If the random seed value is 0, then you will get different samples/outputs each time you run the analysis.

Examples

The following examples are in the Examples folder.
  • Write down the names of all the participants in your class in the population column and randomly select 5 participants from this list. (Sample Data 1.xlsx).


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