size.ci.ancova2

Computes the sample size for each group required to estimate a mean
difference in a 2-group ANCOVA model with desired confidence interval
precision. 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 of all covariates. In an
experiment, this standardized mean difference should be 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.ci.ancova2 function

<dl><dt>alpha</dt>
<dd>alpha level for 1-alpha confidence</dd>
<dt>evar</dt>
<dd>planning value of within group (error) variance</dd>
<dt>s</dt>
<dd>number of covariates</dd>
<dt>d</dt>
<dd>largest standardized mean difference of all covariates</dd>
<dt>w</dt>
<dd>desired confidence interval width</dd>
<dt>R</dt>
<dd>ratio of n2/n1</dd></dl>

Arguments

Sample size for a 2-group ANCOVA confidence interval — size.ci.ancova2

<dl>

<dt>alpha</dt>
<dd>alpha level for 1-alpha confidence</dd>


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


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


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


<dt>w</dt>
<dd>desired confidence interval width</dd>


<dt>R</dt>
<dd>ratio of n2/n1</dd>

</dl>

size.ci.ancova2: Sample size for a 2-group ANCOVA confidence interval

Description

Usage

Value

Arguments

Examples