nonlinear_quantlim: Calculation of the LOB and LOD with a nonlinear fit

Description Usage Arguments Details Warning Author(s) References Examples

View source: R/nonlinear_quantlim.R

Description

This function calculates the value of the LOB (limit of blank) and LOD (limit of detection) from the (Concentration, Intensity) spiked in data. This function should be used instead of the linear function whenever a significant threshold is present at low concentrations. Such threshold is characterized by a signal that is dominated by noise where the mean intensity is constant and independent of concentration. The function also returns the values of the nonlinear curve fit that allows it to be plotted. At least 2 blank samples (characterized by Intensity = 0) are required by this function which are used to calculate the background noise. The LOB is defined as the concentration at which the value of the nonlinear fit is equal to the 95% upper bound of the noise. The LOD is the concentration at which the latter is equal to the 90% lower bound (5% quantile) of the prediction interval of the nonlinear fit. A weighted nonlinear fit is used with weights for every unique concentration proportional to the inverse of variance between replicates. The details behind the calculation of the nonlinear fit can be found in the Reference.

Usage

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nonlinear_quantlim(datain, alpha = 0.05, Npoints = 100, Nbootstrap = 500)	

Arguments

datain

Data frame that contains the input data. The input data frame has to contain the following columns : CONCENTRATION, INTENSITY (both of which are measurements from the spiked in experiment) and NAME which designates the name of the assay (e.g. the name of the peptide or protein)

alpha

Probability level to estimate the LOB/LOD

Npoints

Number of points to use to discretize the concentration line between 0 and the maximum spiked concentration

Nbootstrap

Number of bootstrap samples to use to calculate the prediction interval of the fit. This number has to be increased for very low alpha values or whenever very accurate assay characterization is required.

Details

Warning

The LOB and LOD can only be calculated when more than 2 blank samples are included. The data should ideally be plotted using the companion function plot_quantlim to ensure that the fit is suited to the data.

Author(s)

Cyril Galitzine, Olga Vitek.

Maintainer: Cyril Galitzine (cyrildgg@gmail.com), Meena Choi (mnchoi67@gmail.com)

References

C. Galitzine et al. TBD 2016

Examples

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# Consider data from a spiked-in contained in an example dataset. This dataset contains 
# a significant threshold at low concentrations that is not well captured by a linear fit

head(SpikeInDataNonLinear)

# Call function
nonlinear_quantlim_out <- nonlinear_quantlim(SpikeInDataNonLinear)

#Get values of LOB/LOD
nonlinear_quantlim_out$LOB[1]
nonlinear_quantlim_out$LOD[1]

lindsaypino/MSstats-patch documentation built on May 24, 2019, 6 p.m.