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-\name{loq}
-\alias{loq}
-\alias{loq.lm}
-\alias{loq.rlm}
-\alias{loq.default}
-\title{Estimate a limit of quantification (LOQ)}
-\usage{
- loq(object, \dots, alpha = 0.05, k = 3, n = 1, w.loq = "auto",
- var.loq = "auto")
-}
-\arguments{
- \item{object}{
- A univariate model object of class \code{\link{lm}} or
- \code{\link[MASS:rlm]{rlm}}
- with model formula \code{y ~ x} or \code{y ~ x - 1},
- optionally from a weighted regression. If weights are specified
- in the model, either \code{w.loq} or \code{var.loq} have to
- be specified.
- }
- \item{alpha}{
- The error tolerance for the prediction of x values in the calculation.
- }
- \item{\dots}{
- Placeholder for further arguments that might be needed by
- future implementations.
- }
- \item{k}{
- The inverse of the maximum relative error tolerated at the
- desired LOQ.
- }
- \item{n}{
- The number of replicate measurements for which the LOQ should be
- specified.
- }
- \item{w.loq}{
- The weight that should be attributed to the LOQ. Defaults
- to one for unweighted regression, and to the mean of the weights
- for weighted regression. See \code{\link{massart97ex3}} for
- an example how to take advantage of knowledge about the
- variance function.
- }
- \item{var.loq}{
- The approximate variance at the LOQ. The default value is
- calculated from the model.
- }
-}
-\value{
- The estimated limit of quantification for a model used for calibration.
-}
-\description{
- The limit of quantification is the x value, where the relative error
- of the quantification given the calibration model reaches a prespecified
- value 1/k. Thus, it is the solution of the equation
- \deqn{L = k c(L)}{L = k * c(L)}
- where c(L) is half of the length of the confidence interval at the limit L
- (DIN 32645, equivalent to ISO 11843). c(L) is internally estimated by
- \code{\link{inverse.predict}}, and L is obtained by iteration.
-}
-\note{
- - IUPAC recommends to base the LOQ on the standard deviation of the signal
- where x = 0.
- - The calculation of a LOQ based on weighted regression is non-standard
- and therefore not tested. Feedback is welcome.
-}
-\examples{
-data(massart97ex3)
-attach(massart97ex3)
-m <- lm(y ~ x)
-loq(m)
-
-# We can get better by using replicate measurements
-loq(m, n = 3)
-}
-\seealso{
- Examples for \code{\link{din32645}}
-}
-\keyword{manip}

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