size.ci.mean2

Computes the sample size for each group required to estimate a population
mean difference with desired confidence interval precision in a 2-group
design. Set the variance planning value to the largest value within a
plausible range for a conservatively large sample size. Set R = 1 for
equal sample sizes. For unequal sample sizes, this function assumes
approximately equal population variances.
For more details, see Section 2.13 of Bonett (2021, Volume 1)

Implements confidence interval and sample size methods that are especially
useful in psychological research but are also useful in educational, social science,
business, and biological research. This package includes more than 100 confidence
interval functions and more than 80 sample size functions for 1-group, 2-group,
paired-samples, and multiple-group designs and for a variety of parameters including
means, medians, proportions, slopes, standardized mean differences, standardized
linear contrasts of means, and several measures of correlation and association. 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 about these methods 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.mean2 function

<dl><dt>alpha</dt>
<dd>alpha level for 1-alpha confidence</dd>
<dt>var</dt>
<dd>planning value of average within-group variance</dd>
<dt>w</dt>
<dd>desired confidence interval width</dd>
<dt>R</dt>
<dd>n2/n1 ratio</dd></dl>

Arguments

Sample size for a 2-group mean difference confidence interval — size.ci.mean2

<dl>

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


<dt>var</dt>
<dd>planning value of average within-group variance</dd>


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


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

</dl>

size.ci.mean2: Sample size for a 2-group mean difference confidence interval

Description

Usage

Value

Arguments

References

Examples