t-Test and U-Test

Tip: Stats is a MAXQDA Analytics Pro module and cannot be purchased separately. Therefore, it can only be used via an existing MAXQDA Analytics Pro license and activated through its corresponding serial number. If you already have a MAXQDA Analytics Pro license, Stats is a tab on the main ribbon menu.

In order to conduct a t-test or U-test for independent samples with MAXQDA Stats, select Compare Groups > t-Test for Independent Samples or Compare Groups > Mann-Whitney U-Test for Independent Samples in the main menu. A window will appear which will allow you to select several dependent variables, as well as one comparison factor for the two groups.

Dialog for selecting the dependent variable and the grouping factor for t-test or U-test

Variables can be selected in several ways:

  • Double-click on a variable.
  • Drag and drop the variable into the right window pane.
  • Select one or multiple variables with the mouse by holding the Ctrl/Cmd key then dragging the selection into the right window pane with the mouse, or click the blue arrow in the middle of the window.

To integrate code frequencies per document as dependent variables or as a factor, switch to the “Codes” tab and select the desired codes. (This option is available only if MAXQDA Stats was launched with the data in the MAXQDA project).

Hint: You can only select variables of the type integer or decimal as dependent variable.

Once you have selected a variable or code for defining the groups, you can select a value for defining the groups in each of the Group 1 and Group 2 drop-down menus.

In order to integrate only those cases that contain variables with a valid value select Exclude cases listwise.

After starting the calculation by clicking OK a t-test or U-test is performed for each selected dependent variable.

Results table of the t-test

For the t-test, the following results table appears for the first dependent variable. By using the blue arrows and the drop-down list at the top of the window, you can switch to the results for the other dependent variables.

Results table for the t-test

The results table contains the following information:

  • The number of valid and missing cases for each calculated test is shown in the upper right corner.
  • The first row shows the results for the assumption of homogeneous variances in the two groups. The second row contains the results assuming heterogeneous variances (Welch correction).
  • The effect sizes Cohen’s d and Hedge’s g* help to assess the size of the difference in means.
  • Levene’s test, the results of which are presented in the middle panel, can be used to assess the variance homogeneity of the two groups.
  • In the lower area, the number of cases (N) as well as the mean, standard deviation, and standard error are displayed separately for both groups.
  • Shapiro-Wilk value and the corresponding p-values can be used to check the assumption of a normal distribution in the individual groups.
Note: For the calculation of Cohen’s d, the pooled standard deviation of both groups is used.

Hedges g* applies an additional correction to Cohens d:

Results table of the U-test

For the U-test, the following results table appears for the first dependent variable. Using the blue arrows and the drop-down list at the top of the window, you can switch to the results for the other dependent variables.

Results table for the U-test

In the upper area of the results table, descriptive statistics are presented separately for the two groups, in addition to the number of cases, the median and the mean.

In the lower area, the calculated p-values are displayed.

Note: P-values for small group sizes from 5 to 15 are determined using tabulated values. For larger groups, an approximation is performed. Further notes can be found here:
https://www.alglib.net/hypothesistesting/mannwhitneyu.php

Overview of toolbar functions

The toolbar in the upper section of the results window offers important functions:

Table view/Chart view – switches between the result table and scatter plots.

   Previous/Next – using the blue arrow or the selection list, switch between the results table for the dependent variables.

Refresh – recalls the dialog for selection of variables for the correlation table.

Insert into output viewer – inserts the currently displayed table or chart in the Output Viewer.

Insert all into output viewer – inserts all created tables or charts in the Output Viewer.

Send to QTT worksheet - inserts the current view into a new or an existing QTT worksheet.

Copy – copies the current table, highlighted area in the table, or chart, for example for insertion into Word.

Print – prints the currently displayed table or chart.

Export – exports the currently displayed table in Excel format, website (HTML) format or RTF format for Word and other word processing programs; exports the currently displayed chart in PNG, SVG or EMF (only Windows) format.

Transfer results table to the Output Viewer

After the tables have been created, they can be transferred to the Output Viewer from which they can later be exported together:

  • Click the Insert into output viewer icon to transfer the currently displayed results table to the Output Viewer.
  • Click the Insert all result tables into output viewer icon to transfer all created tables to the Output Viewer at once.
Tip: When the table is transferred, the adjusted column widths will be maintained.

Results table in the Output Viewer

Transfer results to Questions – Themes – Theories

In the Questions – Themes – Theories window, you can collect and comment on all the important results of your project. Click the Send to QTT Worksheet icon in the upper right corner to save the current view in a new or existing worksheet.

Export and print results table

Several options for exporting and printing the currently displayed results table are available using the following symbols:

Copy – copies the entire table or selection to the clipboard, for example in order to paste it directly into Word.

Print – starts the print process and displays a print preview, in which the settings such as margins, orientation, headers and footers can be applied.

Export – exports the table in Excel format, website (HTML) format or RTF format for Word and other word processing programs.

Display means/medians as chart

In order to display a chart of the means or medians of the compared groups click the icon Chart view in the results table.

Chart view

You can customize the design and view of the chart by using the icons in the toolbar above the chart as well as double-clicking and right-clicking the elements of the chart. The chart’s size automatically adjusts to the window size. Enlarge the window in order to receive a larger chart.

Hint: In case of the occurrence of negative means or medians no chart is displayed.

The charts can be transferred to the Output Viewer for storage and later export, or they can be transferred to a QTT worksheet. To do this, click on the corresponding icons in the top right corner of the toolbar:

Insert into Output Viewer and Send to QTT Worksheet.

Hint: Charts will be inserted into the Output Viewer in the size that they are displayed, to a maximum width of 650 pixels.

To export or print a chart directly, you can use the usual icons in the top right of the window:

Copy, Print and Export.

Was this article helpful?