PARAMETERS Subcommand (POWER MEANS INDEPENDENT command)

PARAMETERS controls the test assumptions. The keywords specify the sample sizes, population standard deviations, the population means under testing, and the effect size.

POWER = value(s)

Optional keyword that specifies the desired power level(s). There is no default. Multiple values can be specified with each value separated by a blank space (or blank spaces). A grid of power values from value1 to value2 with the increment of value3, connected by the keywords TO and BY, can also be specified. When a grid of power values is specified, only one valid set of [value1 TO value2 BY value3] is allowed. Value1 and value2 must satisfy the condition 0 < value1 ≤ value2 < 1. The case where value1 = value2 is equivalent to specifying a single value1, regardless of value3. In order to restrict the number of power values, value3 must satisfy the condition

0.01 ≤ value3 <
1

. The grid can be mixed with other power values, and can be placed anywhere.

Notes:

All specified values must be in the range [0,1].
In cases where duplicate values are specified, only unique values are used, and a warning message is generated to indicate that all duplicate values are excluded from the analysis.

TEST = {NONDIRECTIONAL}{DIRECTIONAL}: An optional keyword that determines whether the test is one or two-sided. NONDIRECTIONAL, or a two-sided test, is the default setting. When DIRECTIONAL is specified, power is computed for a one-sided test.
SIGNIFICANCE = value: An optional keyword that specifies the significance level of the Type I error rate for the test. The value must be a single double value ∈(0,1). The default level is 0.05.
N = {integer1 integer2}: A required keyword that specifies the sample size for the two groups for comparison. The values for both integers must be > 1.
NRATIO = {value}: A required keyword that specifies the ratio of the sample sizes. Must be a single value ∈[0.01,100] with 1 as the default setting. The keyword takes effect when POWER is specified, and is ignored when N is specified.
SD = {value}{value1 value2}: A required keyword that specifies the population standard deviation(s). Note that value, value1, and value2 are all numeric values > 0. Multiple parameters value1 and value2, if specified, are separated by a blank space (or blank spaces). When a single value is specified, it denotes the population standard deviation of the group difference σ, and assumes that the two group variances are equal, or σ₁ = σ₂ = σ. When two different values (value1 and value2) are specified, they denote σ₁ and σ₂, respectively.
Note: When two identical value1 and value2 values are specified, the result is the same as a when a single value is specified for the keyword.
MEAN = {value}{value1 value2}: A required keyword that specifies the population mean(s) under testing. Note that value, value1, and value2 are all numeric values. Multiple parameters value1 and value2, if specified, are separated by a blank space (or blank spaces). When a single value is specified, it denotes the population mean difference μ_d. When two values (value1 and value2) are specified, they denote μ₁ and μ₂, respectively.
ES = value: An optional keyword specifies the effect size as an input to the estimation of the power or sample size. When the two independent groups for comparison are assumed to have unequal variances, the effect size of the independent-sample analysis is measured by the mean difference. Must be a single numeric value. When /PARAMETERS TEST = NONDIRECTIONAL, the specified value must be ≥ 0, when POWER is specified, the specified value cannot be 0. When ES is specified, the assumption of equal group variances is automatically made (this influences the /PLOT ES, ES_YAXIS, and ES_XAXIS settings).
Note: ES cannot be specified together with SDor MEAN.