size.test.ancova2

Computes the sample size for each group required to test a mean difference
in an ANCOVA model with desired power in a 2-group design. In a
nonexperimental design, the sample size is affected by the magnitude of
covariate mean differences across groups. The covariate mean differences can
be approximated by specifying the largest standardized covariate mean
difference across of all covariates. In an experiment, this standardized
mean difference is set to 0. Set the error variance planning value to the
largest value within a plausible range for a conservatively large sample
size.

Implements confidence interval and sample size methods that
are especially useful in psychological research. The methods can be
applied in 1-group, 2-group, paired-samples, and multiple-group designs
and to a variety of parameters including means, medians, proportions,
slopes, standardized mean differences, standardized linear contrasts
of means, plus several measures of correlation and association.
Confidence interval and sample size functions are given for single
parameters as well as differences, ratios, and linear contrasts of
parameters. The sample size functions can be used to approximate the
sample size needed to estimate a parameter or function of parameters
with desired confidence interval precision or to perform a variety of
hypothesis tests (directional two-sided, equivalence, superiority,
noninferiority) with desired power. For details see: Statistical Methods
for Psychologists, Volumes 1 – 4, <https://dgbonett.sites.ucsc.edu/>.

Douglas G. Bonett

statpsych

Statistical Methods for Psychologists

Robert J. Calin-Jageman

size.test.ancova2 function

<dl><dt>alpha</dt>
<dd>alpha level for hypothesis test</dd>
<dt>pow</dt>
<dd>desired power</dd>
<dt>evar</dt>
<dd>planning value of within-group (error) variance</dd>
<dt>es</dt>
<dd>planning value of mean difference</dd>
<dt>s</dt>
<dd>number of covariates</dd>
<dt>d</dt>
<dd>largest standardized mean difference of all covariates</dd>
<dt>R</dt>
<dd>n2/n1 rartio</dd></dl>

Arguments

Sample size for a 2-group ANCOVA hypothesis test — size.test.ancova2

<dl>

<dt>alpha</dt>
<dd>alpha level for hypothesis test</dd>


<dt>pow</dt>
<dd>desired power</dd>


<dt>evar</dt>
<dd>planning value of within-group (error) variance</dd>


<dt>es</dt>
<dd>planning value of mean difference</dd>


<dt>s</dt>
<dd>number of covariates</dd>


<dt>d</dt>
<dd>largest standardized mean difference of all covariates</dd>


<dt>R</dt>
<dd>n2/n1 rartio</dd>

</dl>

size.test.ancova2: Sample size for a 2-group ANCOVA hypothesis test

Description

Usage

Value

Arguments

Examples