MeanCIn: Sample Size for a Given Width of a Confidence Interval for a...
In DescTools: Tools for Descriptive Statistics

MeanCIn

R Documentation

Sample Size for a Given Width of a Confidence Interval for a Mean

Description

Returns the required sample size to obtain a given width of a confidence interval for the sample mean. The function uses uniroot() to find a numeric solution. The t distribution is used.

Usage

MeanCIn(ci, sd, interval = c(2, 100000), conf.level = 0.95, 
        norm = FALSE, tol = .Machine$double.eps^0.5)

Arguments

`ci`	the left and right bound of the interval, which is presumed to be symmetric.
`sd`	the standard deviation of the sample.
`interval`	the interval for the sample size to be searched into, (default is c(2, 100000)).
`conf.level`	confidence level, defaults to `0.95`.
`norm`	logical, determining if the t- or normaldistribution should be used.
`tol`	the desired accuracy (convergence tolerance).

Details

The required sample sizes for a specific width of confidence interval for the mean depends recursively on the sample size, as the samplesize defines the degrees of freedom in the t-distribution. Although in most practical cases it will be sufficient to use the normal distribution, we might be interested in exact results.