Sample size or precision for limit of agreement on Bland-Altman plots

prec_lim_agree returns the sample size or the precision for the limit of agreement, i.e. the confidence interval around the limit of agreement, expressed in SD-units. It is an approximation based on the Normal distribution, instead of a Student t distribution.

Usage

prec_lim_agree(n = NULL, conf.width = NULL, conf.level = 0.95)

Arguments

n

sample size.

conf.width

precision (the full width of the confidence interval).

conf.level

confidence level.

Value

Object of class "presize", a list of arguments (including the computed one) augmented with method and note elements.

Details

Exactly one of the parameters n or conf.width must be passed as NULL, and that parameter is determined from the other.

The sample size and precision are calculated according to formulae in Bland & Altman (1986). The CI width is a simple function of the sample size only.

References

Bland & Altman (1986) Statistical methods for assessing agreement between two methods of clinical measurement Lancet i(8476):307-310 doi:10.1016/S0140-6736(86)90837-8

Examples

# calculate confidence interval width, given N
prec_lim_agree(200)
#> 
#>      precision for limit of agreement 
#> 
#>     n conf.width conf.level
#> 1 200  0.4800912       0.95
# calculate N given, confidence interval width
prec_lim_agree(conf.width = .1)
#> 
#>      sample size for limit of agreement 
#> 
#>          n conf.width conf.level
#> 1 4609.751        0.1       0.95