Planned Contrast: Effects Calculation
Click the Calculate Es button in either the Planned Contrast: Power Calculation Parameters dialog box or the Planned Contrast: Sample Size Parameters dialog box, or click the Enter Weights button in the Planned Contrast: Interval Estimation dialog box to display the Planned Contrast: Effects Calculation dialog box.
In this dialog box, you can enter values for cell means, contrast weights, and the population standard deviation, and STATISTICA will compute measures of effect needed to calculate power. In addition, this dialog box provides facilities for importing or exporting cell means and contrast weights to and from spreadsheets, or via the Clipboard.
- Spreadsheet
- Use the options under Spreadsheet to create or open spreadsheets.
- Create
- Click the Create button to create a spreadsheet with the current values of the means and contrast weights, and sigma.
- Open
- Click the Open button to display a standard file selection dialog box to open a previously saved spreadsheet with means, contrast weights, and Sigma. This spreadsheet should be one previously saved in this menu or formatted in the same style. The spreadsheet is opened in a separate window, and its contents are read into the appropriate fields of the Contrast Specification group. If a spreadsheet with an inappropriate format is opened, unpredictable results occur.
The Contrast Specification group has an "automatic resizing" capability. If you open a spreadsheet whose number of groups is different from the number of groups currently specified, the grid in the Contrast Specification box automatically resizes, and the No. of Groups field is adjusted accordingly.
- Clipboard
- Use the options under Clipboard to copy values to or paste values from the Clipboard.
- Copy
- Click the Copy button to copy the means and contrast weights to the Clipboard.
- Paste
- Click the Paste button to copy an array with two columns from the Clipboard to the group means and contrast weights. This function also has an "automatic resizing" capability, so that if the number of rows in the array on the Clipboard does not match the current size of the grid in the Contrast Specification box, the grid is resized automatically to accommodate the array.
- Contrast Specification
- Under Contrast Specification, enter values for the group means and contrast weights associated with a particular contrast, and the population standard deviation. As you enter values for these parameters, STATISTICA automatically updates values for SSWeights, Psi, and Es (see below).
- Sigma
- In the Sigma box, enter the value for the population standard deviation common to all the groups.
- Mean
- In the Mean box, enter a value for the population mean for each group.
- Contrast Weight
- In the Contrast Weight boxes, enter the contrast weight for each group. The default contrast weights are set up to test the hypothesis that the mean of the last group is equal to the average of the means of all the other groups.
- SS Weights
- This is the sum of the squares of the contrast weights. This value, which is required for power, sample size, and interval estimation calculations, is updated automatically as new contrast weights are entered.
- Psi
- This is the actual value of the contrast. This value is updated automatically as new contrast weights or group means are entered.
- Es
- This is the standardized effect size.