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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", tol = "default")
+}
+\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.
+  }
+  \item{tol}{
+    The default tolerance for the LOQ on the x scale is the value of the
+    smallest non-zero standard divided by 1000. Can be set to a 
+    numeric value to override this.
+  }
+}
+\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}