The POWER Procedure
- Overview
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Getting Started
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Syntax
PROC POWER Statement LOGISTIC Statement MULTREG Statement ONECORR Statement ONESAMPLEFREQ Statement ONESAMPLEMEANS Statement ONEWAYANOVA Statement PAIREDFREQ Statement PAIREDMEANS Statement PLOT Statement TWOSAMPLEFREQ Statement TWOSAMPLEMEANS Statement TWOSAMPLESURVIVAL Statement TWOSAMPLEWILCOXON Statement
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Details
Overview of Power Concepts Summary of Analyses Specifying Value Lists in Analysis Statements Sample Size Adjustment Options Error and Information Output Displayed Output ODS Table Names Computational Resources Computational Methods and Formulas ODS Graphics ODS Styles Suitable for Use with PROC POWER
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Examples
One-Way ANOVA The Sawtooth Power Function in Proportion Analyses Simple AB/BA Crossover Designs Noninferiority Test with Lognormal Data Multiple Regression and Correlation Comparing Two Survival Curves Confidence Interval Precision Customizing Plots Binary Logistic Regression with Independent Predictors Wilcoxon-Mann-Whitney Test
- References
| PAIREDFREQ Statement |
The PAIREDFREQ statement performs power and sample size analyses for McNemar’s test for paired proportions.
Summary of Options
Table 70.14 summarizes categories of options available in the PAIREDFREQ statement.
Task |
Options |
|---|---|
Define analysis |
|
Specify analysis information |
|
Specify effects |
|
Specify sample size |
|
Specify power |
|
Control sample size rounding |
|
Choose computational method |
|
Control ordering in output |
Table 70.15 summarizes the valid result parameters in the PAIREDFREQ statement.
Analyses |
Solve For |
Syntax |
|---|---|---|
Power |
||
Sample size |
||
Power |
||
Power |
||
Sample size |
Dictionary of Options
- ALPHA=number-list
specifies the level of significance of the statistical test. The default is 0.05, corresponding to the usual 0.05
100% = 5% level of significance. See the section Specifying Value Lists in Analysis Statements for information about specifying the number-list. - CORR=number-list
specifies the correlation
between members of a pair. See the section Specifying Value Lists in Analysis Statements for information about specifying the number-list. - DISCPROPORTIONS=grouped-number-list
- DISCPS=grouped-number-list
specifies the two discordant proportions,
and 
. See the section Specifying Value Lists in Analysis Statements for information about specifying the grouped-number-list. - DISCPROPDIFF=number-list
- DISCPDIFF=number-list
specifies the difference
between discordant proportions. See the section Specifying Value Lists in Analysis Statements for information about specifying the number-list. - DISCPROPRATIO=number-list
- DISCPRATIO=number-list
specifies the ratio
of discordant proportions. See the section Specifying Value Lists in Analysis Statements for information about specifying the number-list. - DIST=EXACT_COND
- DIST=NORMAL
specifies the underlying distribution assumed for the test statistic. EXACT_COND corresponds to the exact conditional test, based on the exact binomial distribution of the two types of discordant pairs given the total number of discordant pairs. NORMAL corresponds to the conditional test based on the normal approximation to the binomial distribution of the two types of discordant pairs given the total number of discordant pairs. The default value is EXACT_COND.
- METHOD=CONNOR
- METHOD=EXACT
- METHOD=MIETTINEN
specifies the computational method. METHOD=EXACT (the default) uses the exact binomial distributions of the total number of discordant pairs and the two types of discordant pairs. METHOD=CONNOR uses an approximation from Connor (1987), and METHOD=MIETTINEN uses an approximation from Miettinen (1968). The CONNOR and MIETTINEN methods are valid only for DIST=NORMAL.
- NFRACTIONAL
- NFRAC
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. This option cannot be used with METHOD=EXACT.
- NPAIRS=number-list
specifies the total number of proportion pairs (concordant and discordant) or requests a solution for the number of pairs with a missing value (NPAIRS=.). See the section Specifying Value Lists in Analysis Statements for information about specifying the number-list.
- NULLDISCPROPRATIO=number-list
- NULLDISCPRATIO=number-list
- NULLRATIO=number-list
- NULLR=number-list
specifies the null value of the ratio of discordant proportions. The default value is 1. See the section Specifying Value Lists in Analysis Statements for information about specifying the number-list.
- ODDSRATIO=number-list
- OR=number-list
specifies the odds ratio
. See the section Specifying Value Lists in Analysis Statements for information about specifying the number-list. - OUTPUTORDER=INTERNAL
- OUTPUTORDER=REVERSE
- OUTPUTORDER=SYNTAX
-
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:
TOTALPROPDISC=
The OUTPUTORDER=SYNTAX option arranges the parameters in the output in the same order in which their corresponding options are specified in the PAIREDFREQ 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 PAIREDFREQ statement.
- PAIREDPROPORTIONS=grouped-number-list
- PPROPORTIONS=grouped-number-list
- PAIREDPS=grouped-number-list
- PPS=grouped-number-list
specifies the two paired proportions,
and 
. See the section Specifying Value Lists in Analysis Statements for information about specifying the grouped-number-list. - POWER=number-list
specifies the desired power of the test or requests a solution for the power with a missing value (POWER=.). The power is expressed as a probability, a number between 0 and 1, rather than as a percentage. See the section Specifying Value Lists in Analysis Statements for information about specifying the number-list.
- PROPORTIONDIFF=number-list
- PDIFF=number-list
specifies the proportion difference
. See the section Specifying Value Lists in Analysis Statements for information about specifying the number-list. - REFPROPORTION=number-list
- REFP=number-list
specifies either the reference first proportion
(when used in conjunction with the PROPORTIONDIFF=, ODDSRATIO=, or RELATIVERISK= option) or the reference discordant proportion (when used in conjunction with the DISCPROPDIFF= or DISCPROPRATIO= option). See the section Specifying Value Lists in Analysis Statements for information about specifying the number-list. - RELATIVERISK=number-list
- RR=number-list
specifies the relative risk
. See the section Specifying Value Lists in Analysis Statements for information about specifying the number-list. - SIDES=keyword-list
-
specifies the number of sides (or tails) and the direction of the statistical test or confidence interval. See the section Specifying Value Lists in Analysis Statements for information about specifying the keyword-list. Valid keywords and their interpretation are as follows:
- 1
one-sided with alternative hypothesis in same direction as effect
- 2
two-sided
- U
upper one-sided with alternative greater than null value
- L
lower one-sided with alternative less than null value
If the effect size is zero, then SIDES=1 is not permitted; instead, specify the direction of the test explicitly in this case with either SIDES=L or SIDES=U. The default value is 2.
- TEST=MCNEMAR
specifies the McNemar test of paired proportions. This is the default test option.
- TOTALPROPDISC=number-list
- TOTALPDISC=number-list
- PDISC=number-list
specifies the sum of the two discordant proportions,
. See the section Specifying Value Lists in Analysis Statements for information about specifying the number-list.
Restrictions on Option Combinations
To specify the proportions, choose one of the following parameterizations:
discordant proportions (using the DISCPROPORTIONS= option)
difference and sum of discordant proportions (using the DISCPROPDIFF= and TOTALPROPDISC=options)
difference of discordant proportions and reference discordant proportion (using the DISCPROPDIFF= and REFPROPORTION= options)
ratio of discordant proportions and reference discordant proportion (using the DISCPROPRATIO= and REFPROPORTION= options)
ratio and sum of discordant proportions (using the DISCPROPRATIO= and TOTALPROPDISC=options)
paired proportions and correlation (using the PAIREDPROPORTIONS= and CORR= options)
proportion difference, reference proportion, and correlation (using the PROPORTIONDIFF=, REFPROPORTION=, and CORR= options)
odds ratio, reference proportion, and correlation (using the ODDSRATIO=, REFPROPORTION=, and CORR= options)
relative risk, reference proportion, and correlation (using the RELATIVERISK=, REFPROPORTION=, and CORR= options)
Option Groups for Common Analyses
This section summarizes the syntax for the common analyses supported in the PAIREDFREQ statement.
McNemar Exact Conditional Test
You can express effects in terms of the individual discordant proportions, as in the following statements. Default values for the TEST=, SIDES=, ALPHA=, and NULLDISCPROPRATIO= options specify a two-sided McNemar test for no effect with a significance level of 0.05.
proc power;
pairedfreq dist=exact_cond
discproportions = 0.15 | 0.45
npairs = 80
power = .;
run;
You can also express effects in terms of the difference and sum of discordant proportions:
proc power;
pairedfreq dist=exact_cond
discpropdiff = 0.3
totalpropdisc = 0.6
npairs = 80
power = .;
run;
You can also express effects in terms of the difference of discordant proportions and the reference discordant proportion:
proc power;
pairedfreq dist=exact_cond
discpropdiff = 0.3
refproportion = 0.15
npairs = 80
power = .;
run;
You can also express effects in terms of the ratio of discordant proportions and the denominator of the ratio:
proc power;
pairedfreq dist=exact_cond
discpropratio = 3
refproportion = 0.15
npairs = 80
power = .;
run;
You can also express effects in terms of the ratio and sum of discordant proportions:
proc power;
pairedfreq dist=exact_cond
discpropratio = 3
totalpropdisc = 0.6
npairs = 80
power = .;
run;
You can also express effects in terms of the paired proportions and correlation:
proc power;
pairedfreq dist=exact_cond
pairedproportions = 0.6 | 0.8
corr = 0.4
npairs = 45
power = .;
run;
You can also express effects in terms of the proportion difference, reference proportion, and correlation:
proc power;
pairedfreq dist=exact_cond
proportiondiff = 0.2
refproportion = 0.6
corr = 0.4
npairs = 45
power = .;
run;
You can also express effects in terms of the odds ratio, reference proportion, and correlation:
proc power;
pairedfreq dist=exact_cond
oddsratio = 2.66667
refproportion = 0.6
corr = 0.4
npairs = 45
power = .;
run;
You can also express effects in terms of the relative risk, reference proportion, and correlation:
proc power;
pairedfreq dist=exact_cond
relativerisk = 1.33333
refproportion = 0.6
corr = 0.4
npairs = 45
power = .;
run;
McNemar Normal Approximation Test
The following statements demonstrate a sample size computation for the normal-approximate McNemar test. The default value for the METHOD= option specifies an exact sample size computation. Default values for the TEST=, SIDES=, ALPHA=, and NULLDISCPROPRATIO= options specify a two-sided McNemar test for no effect with a significance level of 0.05.
proc power;
pairedfreq dist=normal method=connor
discproportions = 0.15 | 0.45
npairs = .
power = .9;
run;