size.ci.median

Computes the sample size required to estimate a population median with
desired confidence interval precision. 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.

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.median function

<dl><dt>alpha</dt>
<dd>alpha level for 1-alpha confidence</dd>
<dt>var</dt>
<dd>planning value of response variable variance</dd>
<dt>w</dt>
<dd>desired confidence interval width</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 median confidence interval — size.ci.median

<dl>

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


<dt>var</dt>
<dd>planning value of response variable variance</dd>


<dt>w</dt>
<dd>desired confidence interval width</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.median: Sample size for a median confidence interval

Description

Usage

Value

Arguments

References

Examples