size.ci.median2

Computes the sample size for each group required to estimate a population
median 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. The sample size
requirement depends on the shape of the distribution. Select one of the
four distribution options (Normal, Logistic, Laplace, Exponential) that
approximates the most likely distribution shape in the planned study.
Select the Normal distribution for a conservatively large sample size
requirement. Set R = 1 for equal sample sizes.

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.median2 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>
<dt>dist</dt>
<dd><ul>
<li>set to 1 for Normal distribution (skew = 0, kurtosis = 3)</li>
<li>set to 2 for Logistic distribution (skew = 0, kurtosis = 4.2)</li>
<li>set to 3 for Laplace distribution (skew = 0, kurtosis = 6)</li>
<li>set to 4 for Gamma(5) (skew = .89, kurtosis = 4.2)</li>
<li>set to 5 for Exponential distribution (skew = 2, kurtosis = 9)</li>
</ul></dd></dl>

Arguments

Sample size for a 2-group median difference confidence interval — size.ci.median2

<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>


<dt>dist</dt>
<dd><ul>
<li>set to 1 for Normal distribution (skew = 0, kurtosis = 3)</li>
<li>set to 2 for Logistic distribution (skew = 0, kurtosis = 4.2)</li>
<li>set to 3 for Laplace distribution (skew = 0, kurtosis = 6)</li>
<li>set to 4 for Gamma(5) (skew = .89, kurtosis = 4.2)</li>
<li>set to 5 for Exponential distribution (skew = 2, kurtosis = 9)</li>
</ul></dd>

</dl>

size.ci.median2: Sample size for a 2-group median difference confidence interval

Description

Usage

Value

Arguments

References

Examples