LCX: Predict X% Lethal Concentration at the maximum time point...
In morse: Modelling Reproduction and Survival Data in Ecotoxicology

LCx	R Documentation

Predict `X`% Lethal Concentration at the maximum time point (default).

Description

Predict median and 95% credible interval of the x% Lethal Concentration.

The function LCx, x% Lethal Concentration (LC_x), is use to compute the dose required to kill x% of the members of a tested population after a specified test duration (time_LCx) (default is the maximum time point of the experiment).

Mathematical definition of x% Lethal Concentration at time t, denoted LC(x,t), is:

S(LC(x,t), t) = S(0, t)*(1- x/100),

where S(LC(x,t), t) is the survival probability at concentration LC(x,t) at time t, and S(0,t) is the survival probability at no concentration (i.e. concentration is 0) at time t which reflect the background mortality h_b:

S(0, t) = exp(-hb* t).

In the function LCx, we use the median of S(0,t) to rescale the x% Lethal Concentration at time t.

Usage

LCx(object, ...)

## S3 method for class 'survFit'
LCx(object, X, time_LCx = NULL, conc_range = NULL, npoints = 100, ...)

Arguments

`object`	An object of class `survFit`
`...`	Further arguments to be passed to generic methods
`X`	Percentage of individuals dying (e.g., `50` for `LC_{50}`, `10` for `LC_{10}`, ...)
`time_LCx`	A number giving the time at which `LC_{x}` has to be estimated. If NULL, the latest time point of the experiment is used.
`conc_range`	A vector of length 2 with minimal and maximal value of the range of concentration. If NULL, the range is define between 0 and the highest tested concentration of the experiment.
`npoints`	Number of time point in `conc_range` between 0 and the maximal concentration. 100 by default.

Details

When class of object is survFit, see LCx.survFit.

Value

returns an object of class LCx.

The function returns an object of class LCx, which is a list with the following information:

`X_prop`	Survival probability of individuals surviving considering the median of the background mortality (i.e. `S(0, t)*(1- x/100)`)
`X_prop_provided`	Survival probability of individuals surviving as provided in arguments (i.e. `(100-X)/100)`
`time_LCx`	A number giving the time at which `LC_{x}` has to be estimated as provided in arguments or if NULL, the latest time point of the experiment is used.
`df_LCx`	A `data.frame` with quantiles (median, 2.5% and 97.5%) of `LC_{X}` at time `time_LCx` for `X`% of individuals
`df_dose`	A `data.frame` with four columns: `concentration`, and median `q50` and 95% credible interval (`qinf95` and `qsup95`) of the survival probability at time `time_LCx`