truncated_qqplot {reflimR}

Quantile-Quantile plot of truncated laboratory results

Description

Generates and plots a quantile-quantile plot (q-q plot) with a theoretical normal distribution on the x-axis and the corresponding empirical distribution on the y-axis. Returns intercept, slope, and estimated quantiles 0.025 and 0.975 (i.e., reference limits).

Usage

truncated_qqplot(x.trunc, lognormal = NULL, perc.trunc = 2.5, n.min = 200,
        apply.rounding = TRUE, plot.it = TRUE,
        main = "Q-Q plot",
        xlab = "theoretical quantiles",
        ylab = "sample quantiles")

Arguments

x.trunc

truncated numeric vector of positive numbers, usually generated by iboxplot()

lognormal

Boolean indicating whether a lognormal distribution should be assumed (NULL means that the distribution type is defined automatically)

perc.trunc

percentage of values that has been removed from each side by truncation

n.min

minimal number of values in x.trunc for a robust estimate of reference limits

apply.rounding

Boolean indicating whether the reference limits should be rounded

plot.it

Boolean indicating whether a graphic should be created

main, xlab, ylab

title and labels of the graphic

Details

Intercept and slope of the q-q plot represent the robust mean and standard deviation of x.trunc. They serve as parameters to estimate the reference limits being represented by the quantiles 0.025 and 0.975 of a presumably normal subset of x.

Value

$stats

intercept and slope of the q-q plot, lower and upper truncation points

$lognormal

Boolean indicating whether a lognormal distribution has been assumed

References

1. Hoffmann G et al. Simple estimation of reference intervals from routine laboratory data. J Lab Med 2016. doi:10.1515/labmed-2015-0104.

Examples

set.seed(123)
x <- rlnorm(n = 250, meanlog = 3,  sdlog = 0.3)
x.trunc <- iboxplot(x, plot.it = FALSE)$trunc
truncated_qqplot(x.trunc)

x.f <- subset(livertests, livertests$Sex == "f")
x.trunc <- iboxplot(x.f$ALT, plot.it = FALSE)$trunc
truncated_qqplot(x.trunc, n.min = length(x.trunc), main = "ALT")