Workspace Node: t-Test, Independent, by Groups - Specifications - Quick Tab
The t-Test, Independent, by Groups workspace node can be accessed from the Feature Finder, ribbon bar, or Node Browser. The Quick tab of the specifications dialog box is displayed by default when you double-click the node.
Use the options in this dialog box to compute t-tests for independent samples when the data are entered case by case, that is, to let each row in the data file represent one case (e.g., individual, respondent) and to let each column in the data file represent one variable or measurement (e.g., response to a questionnaire item). In this setup, a grouping variable should be included to denote to which group each case belongs. Use this t-test, Independent, by Groups node if the data are arranged precisely in this manner.
If you have entered the data so that each variable represents the responses of one group, you need to use the t-test for Independent Samples, by Variables node instead. See the t-test for independent samples overview.
| Element Name | Description |
|---|---|
| Variables | Click this button to display a two variable selection dialog box. Specify one grouping variable and a list of dependent variables for the comparison. Statistica computes the t-test for all variables in the dependent variable list, comparing the two groups that are identified by the two selected group codes (see below) in the grouping variable. |
| Code for Group 1 / Code for Group 2 | Specify the two codes that identify the two groups in the grouping variable that are to be compared in the Code for Group 1 and Code for Group 2 fields. If you are not sure about the codes that were used in the grouping variables to identify the groups, double-click on the edit field (or press the F2 key on your keyboard), and the Select a code for grouping dialog box will be displayed containing all integer codes and their alphanumeric equivalents found in the grouping variable in the current data file. You can select a grouping code in this dialog box (i.e., transfer it to the edit field) by double-clicking on it. |
| Weighted moments | Select this check box to specify that each observation contributes the weighting variable's value for that observation. The weight values need not be integers. This module can use fractional case weights in most computations. Some other modules use case weights as integer case multipliers or frequency values. This option is available only after you have defined a weight variable via the W option described below. |
| DF = W-1 / N-1 | When the Weighted moments check box is selected, some statistics related to the moments (e.g., standard deviations and variances, skewness, kurtosis) can be based on the sum of the weight values for the weighting variable (W-1), or on the number of (unweighted) observations (N-1). The sums (and means), and sums of squares and cross products will always be based on the weighted values of the respective observations. However, in computations requiring the degrees of freedom (e.g., standard deviation, t-test, etc.), the value for the degrees of freedom can either be computed as the sum of the weight values minus one, or as the number of observations minus one. Moment statistics (except for the mean) are based on the sum of the weight values for the weighting variable when the W-1 option button is selected, and are based on the number of (unweighted) observations when the N-1 option button is selected. When the Weighted moments check box is selected, several graphics options will not be available. For more information on options for using integer case weights, see also Selecting a Weighting Variable. |
| MD deletion | When Casewise deletion of missing data is selected, Statistica ignores all cases that have missing data for any of the variables selected in the list. When Pairwise deletion of missing data is selected, all valid data points will be included in the analyses for the respective variables (resulting possibly in unequal valid N per variable).
Options / C / W. See Common Options. |
| OK | Click this button to accept all the specifications made in the dialog box and to close it. The analysis results are placed in the Reporting Documents workspace node after running (updating) the project. |
See also, Results - Quick tab, Results - Advanced tab, Results - Options tab, Downstream tab, and Home tab.