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Diffstat (limited to 'trunk/R/loq.R')
-rw-r--r-- | trunk/R/loq.R | 40 |
1 files changed, 40 insertions, 0 deletions
diff --git a/trunk/R/loq.R b/trunk/R/loq.R new file mode 100644 index 0000000..5776096 --- /dev/null +++ b/trunk/R/loq.R @@ -0,0 +1,40 @@ +loq <- function(object, ..., alpha = 0.05, k = 3, n = 1, w.loq = "auto", + var.loq = "auto") +{ + UseMethod("loq") +} + +loq.default <- function(object, ..., alpha = 0.05, k = 3, n = 1, w.loq = "auto", + var.loq = "auto") +{ + stop("loq is only implemented for univariate lm objects.") +} + +loq.lm <- function(object, ..., alpha = 0.05, k = 3, n = 1, w.loq = "auto", + var.loq = "auto") +{ + if (length(object$weights) > 0 && var.loq == "auto" && w.loq == "auto") { + stop(paste("If you are using a model from weighted regression,", + "you need to specify a reasonable approximation for the", + "weight (w.loq) or the variance (var.loq) at the", + "limit of quantification")) + } + xname <- names(object$model)[[2]] + yname <- names(object$model)[[1]] + f <- function(x) { + newdata <- data.frame(x = x) + names(newdata) <- xname + y <- predict(object, newdata) + p <- inverse.predict(object, rep(y, n), ws = w.loq, + var.s = var.loq, alpha = alpha) + (p[["Prediction"]] - k * p[["Confidence"]])^2 + } + tmp <- optimize(f,interval=c(0,max(object$model[[2]]))) + loq.x <- tmp$minimum + newdata <- data.frame(x = loq.x) + names(newdata) <- xname + loq.y <- predict(object, newdata) + loq <- list(loq.x, loq.y) + names(loq) <- c(xname, yname) + return(loq) +} |