exponential: (Shifted) - Exponential distribution of germination times...

In OnofriAndreaPG/drcte: Statistical Approaches for Time-to-Event Data in Agriculture

(Shifted) - Exponential distribution of germination times within a seed lot

Description

This function provides the truncated and shifted exponential cumulative distribution of germination times, to be used to fit time-to-event methods to the time-course of seed germination for a seed lot.

Usage

exponential(fixed = c(NA, NA, NA), names = c("b", "d", "shift"))

Arguments

fixed

numeric vector. Specifies which parameters are fixed and at what value they are fixed. NAs for parameter that are not fixed. It is used to fix the shifting parameter ('shift') to 0, so that this becomes the usual exponential cumulative probability function. It is also used to fix the 'd' parameter to 1, which provides the usual (non-truncated) exponential distribution, with no final fraction of individuals without the event.

names

a vector of character strings giving the names of the parameters. The default is reasonable.

Details

The exponential distribution of event times is parameterised as:

P(t) = d\left[ 1 - \exp(-b (t - shift)) \right]

where 't' is the time and 'P(t)' is the proportion of germinated seeds at time = t.

Value

The value returned is a list containing the nonlinear function, the self starter function and the parameter names.

Author(s)

Andrea Onofri

References

Kleinbaum, D.G., Klein, M., 2005. Survival analysis. Springer Science, USA.

Examples

library(drcte)
data(chickweed)

OnofriAndreaPG/drcte documentation built on April 14, 2025, 10:44 a.m.