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.

## Display

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.

## Seed

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.

## Save

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.

## See also

- 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.