Power Analysis of IndependentSample Binomial Test
This feature requires IBM® SPSS® Statistics Base Edition.
Power analysis plays a pivotal role in a study plan, design, and conduction. The calculation of power is usually before any sample data have been collected, except possibly from a small pilot study. The precise estimation of the power may tell investigators how likely it is that a statistically significant difference will be detected based on a finite sample size under a true alternative hypothesis. If the power is too low, there is little chance of detecting a significant difference, and nonsignificant results are likely even if real differences truly exist.
The binomial distribution is based on a sequence of Bernoulli trials. It can be used to model those experiments including a fixed number of total trials that are assumed to be independent of each other. Each trial leads to a dichotomous result, with the same probability for a "successful" outcome. The independentsample binomial test compares two independent proportion parameters.
 From the menus choose:
 Select a test assumption Estimate setting (Sample size or Power).

When Sample size is selected, enter either a Single power value for sample size estimation value (the value must be a single value between 0 and 1), or select Grid power values and then click Grid to view projected sample sizes for a range of specific Power values.
For more information, see Power Analysis: Grid Values.
Optionally, specify a Group size ratio value. The default value is 1.
 When Power is selected as the test assumption Estimate setting, enter values to specify the Total number of trials for group 1 and group 2. The values must be an integers greater than 1.
 Specify the proportion parameters for the two groups. Both values must be in
the range 0  1.Note: The two values cannot be the same when a Power value is specified.
 Optionally, specify the significance level of the Type I error rate for the test in the Significance level field. The value must be a single double value between 0 and 1. The default value is 0.05.
 Select the desired test method:
 Chisquared test
 Estimates the power based on Pearson's chisquared test. This is the default
setting.
 Standard deviation is pooled
 This optional setting controls whether the estimation of the standard deviation is pooled or unpooled. The setting is enabled by default.
 Apply continuity correction
 This optional setting controls whether or not the continuity correction is used. The setting is disabled by default.
 Ttest
 Estimates the power based on Student's ttest.
 Standard deviation is pooled
 This optional setting controls whether the estimation of the standard deviation is pooled or unpooled. The setting is enabled by default.
 Likelihood ratio test
 Estimates the power based on the likelihood ratio test.
 Fisher's exact test
 Estimates the power based on Fisher's exact test.Notes:
 In some cases, Fisher's exact test may take an extended amount of time to complete.
 All plots are blocked when Fisher's exact test is selected.
 Select a method for estimating the power.
 Normal approximation
 Enables normal approximation. This is the default setting.
 Binomial enumeration
 Enables the binomial enumeration method. Optionally, use the Time limit field to specify the maximum number of minutes allowed to estimate the sample size. When the time limit is reached, the analysis is terminated and a warning message is displayed. When specified, the value must be a single positive integer to denote the number of minutes. The default setting is 5 minutes.
 Select whether the test is one or twosided.
 Nondirectional (twosided) analysis
 When selected, a twosided test is used. This is the default setting.
 Directional (onesided) analysis
 When selected, power is computed for a onesided test.
 You can optionally click Plot to specify Power Analysis of IndependentSamples Binomial Test: Plot settings (chart output, twodimensional plot
settings, and threedimensional plot settings).Note: Plot is available only when Power is selected as the test assumption Estimate and Binomial enumeration is not selected.
 Optionally, click Precision to estimate the sample size based on confidence intervals by specifying the values of the confidence interval halfwidths. For more information, see Power Analysis: Precision.
This procedure pastes POWER PROPORTIONS INDEPENDENT command syntax.