This menu allows you to perform a power analysis for a fixed term or contrast in a REML analysis using the VPOWER procedure.
Fixed term to calculate the power for
The dropdown list contains the fixed terms in the REML model. Select the term you want to calculate the power for.
This controls what output is printed from the analysis:
|Power||The estimated power|
|Number of failures||The number of bootstrap samples whose analysis failed to converge|
|Monitoring||Monitoring information, showing the progress of the bootstrap sampling|
Type of test
Specifies the type of test. You can select the following types:
|F ratio||Use the F ratio with an F test to assess the significance of the term|
|Wald||Use the Wald statistic with a chi-square test to assess the significance of the term|
|Two sided||Use a contrast with a two-sided test to assess if the term differs from zero|
|Greater than||Use a contrast with a one-sided test to assess if the term is greater than zero|
|Less than||Use a contrast with a one-sided test to assess if the term is less than zero|
|Equivalence||Use a contrast with a one-sided test to assess if the term is not significantly different from zero. For example, if the treatments have a difference c, the null hypothesis that the treatments are not equivalent is that either: c ≤ – size of difference or c) ≥ – size of difference|
|Non-inferiority||Use a contrast with a one-sided test to assess if the term does not differ significantly from zero. For example, if the treatments have a difference c, to demonstrate non-inferiority of treatment 1 compared to treatment 2, the null hypothesis becomes: c ≥ -size of difference which represents a simple one-sided t-test|
Note that apart from types F ratio and Wald, you need to specify the contrast between treatment means that you are examining with the Define Contrast dialog.
Significance level (alpha)%
Significance level as a percentage (0-100) at which the response is required to be detected; default 5%.
Size of the difference to be detected
Size of the difference between the treatment effects that is to be detected.
Specific critical value
If this is selected, then the value provided in the field will be used as the critical value for the test statistic (F ratio, Wald or t). If this is not specified the critical value will obtained from the usual F, chi-square or t-distribution, according to the type of test and estimated degrees of freedom.
Number of samples
This option specifies the number of bootstrap samples that are performed, default 99 (as well as the “null” sample where the data keep their original values).
Number of retries
This option specifies the number of extra samples that are performed when the REML model does not converge for a bootstrap sample, default 99.
Specifies the seed for the random number generator used to make the bootstrap samples; default 0 continues from the previous generation or (if none) initializes the seed automatically.
Use this option to save the calculated power. After selecting the Power box, you need to type the identifier of a scalar into the In: field.
- Further Output for obtaining additional output after fitting a model.
- Define Contrast dialog for specifying the contrast the power is to be calculated for.
- VPOWER procedure to calculate the power in a REML model.
- APOWER procedure to calculate the power in an analysis of variance.
- RPOWER procedure to calculate the power in a regression analysis.
- Linear Mixed Model menu.
- Initial Values for specifying initial gamma.
- Save for saving the results from a REML analysis.
- Save REML results in a spreadsheet.
- Residual Plots for generating plots of residuals.
- Means Plots for generating plots of one- or two-way tables of means.
- REML directive for command mode use of REML, with additional options to
control the algorithm and for more sophisticated analyses.
- VCOMPONENTS directive for further information about fixed, random, and spline model terms.
- Linear Mixed Models (REML) – Correlated Errors for setting up covariance models.
- REML Detect Outliers dialog for identifying outliers.
- REML Permutation Test dialog for calculating the significance of a random term using a permutation test.