POWER Statement 
The POWER statement performs power and sample size analyses for the Type III test of each effect in the model defined by the MODEL statements and for the contrasts defined by all CONTRAST statements. The MODEL statement must appear before the POWER statement if the EFFECTS option is used in the POWER statement.
Table 43.4 summarizes categories of options available in the POWER statement.
Task 
Options 

Specify effects 

Specify significance level 

Specify covariates 

Specify error standard deviation 

Specify sample size 

Specify power 

Control sample size rounding 

Control ordering in output 

Table 43.5 summarizes the valid result parameters.
Solve for 
Syntax 

Power 
POWER = . 
Sample size 
NTOTAL = . 
specifies the level of significance of each test. The default is 0.05, corresponding to the usual 0.05 100% = 5% level of significance. Note that this is a testwise significance level with the same value for all tests, not incorporating any corrections for multiple testing. See the section Specifying Value Lists in the POWER Statement for information about specifying the numberlist.
specifies the multiple correlation () between all covariates and the response. The error standard deviation given by the STDDEV= option is consequently reduced by multiplying it by a factor of , provided that the number of covariates (as determined by the NCOVARIATES= option) is greater than zero. You cannot use the CORRXY= and the PROPVARREDUCTION= options simultaneously. See the section Specifying Value Lists in the POWER Statement for information about specifying the numberlist.
specifies the location of the Dependent column in the output when the OUTPUTORDER=REVERSE option or OUTPUTORDER=SYNTAX option is used, according to its relative position in the POWER statement.
specifies the model effects to include in the power analysis. By default, or if the EFFECTS keyword is specified without the equal sign (=), all model effects are included. Specify EFFECTS=() to exclude all model effect tests from the power analysis. You can include main effects and interactions by using the effects notation of PROC GLM; see the section Specification of Effects in Chapter 41, The GLM Procedure for further details. The MODEL statement must appear before the POWER statement if the EFFECTS option is used.
specifies the number of additional degrees of freedom to accommodate covariate effects—both class and continuous—not listed in the MODEL statement. The error degrees of freedom are consequently reduced by the value of the NCOVARIATES= option, and the error standard deviation (whose unadjusted value is provided with the STDDEV= option) is reduced according to the value of the CORRXY= or PROPVARREDUCTION= option. See the section Specifying Value Lists in the POWER Statement for information about specifying the numberlist.
enables fractional input and output for sample sizes. See the section Sample Size Adjustment Options for information about the ramifications of the presence (and absence) of the NFRACTIONAL option.
specifies the sample size or requests a solution for the sample size with a missing value (NTOTAL=.). Values for the sample size must be no smaller than the model degrees of freedom (counting the covariates). See the section Specifying Value Lists in the POWER Statement for information about specifying the numberlist.
controls how the input and default analysis parameters are ordered in the output. OUTPUTORDER=INTERNAL (the default) arranges the parameters in the output according to the following order of their corresponding options:
weight variable (from the WEIGHT statement)
The OUTPUTORDER=SYNTAX option arranges the parameters in the output in the same order in which their corresponding options are specified in the POWER statement. The OUTPUTORDER=REVERSE option arranges the parameters in the output in the reverse of the order in which their corresponding options are specified in the POWER statement.
specifies the desired power of each test or requests a solution for the power with a missing value (POWER=.). The power is expressed as a probability (for example, 0.9) rather than a percentage. Note that this is a testwise power with the same value for all tests, without any correction for multiple testing. See the section Specifying Value Lists in the POWER Statement for information about specifying the numberlist.
specifies the proportional reduction () in total incurred by the covariates—in other words, the amount of additional variation explained by the covariates. The error standard deviation given by the STDDEV= option is consequently reduced by multiplying it by a factor of , provided that the number of covariates (as determined by the NCOVARIATES= option) is greater than zero. You cannot use the PROPVARREDUCTION= and the CORRXY= options simultaneously. See the section Specifying Value Lists in the POWER Statement for information about specifying the numberlist.
specifies the error standard deviation, or root MSE. If covariates are specified using the NCOVARIATES= option, then the STDDEV= option denotes the error standard deviation before accounting for these covariates. See the section Specifying Value Lists in the POWER Statement for information about specifying the numberlist.
For the relationship between covariates and response, specify either the multiple correlation (by using the CORRXY= option) or the proportional reduction in total (by using the PROPVARREDUCTION= option).