size.ci.lc.ancova

Computes the sample size for each group (assuming equal sample sizes)
required to estimate a population linear contrast of means in an 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 across all
pairwise group differences and for 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.lc.ancova 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 for all covariates</dd>
<dt>w</dt>
<dd>desired confidence interval width</dd>
<dt>v</dt>
<dd>vector of between-subjects contrast coefficients</dd></dl>

Arguments

Sample size for a linear contrast confidence interval in an ANCOVA — size.ci.lc.ancova

<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 for all covariates</dd>


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


<dt>v</dt>
<dd>vector of between-subjects contrast coefficients</dd>

</dl>

size.ci.lc.ancova: Sample size for a linear contrast confidence interval in an ANCOVA

Description

Usage

Value

Arguments

Examples