telfer: Telfer's change index

In BiologicalRecordsCentre/sparta: Trend Analysis for Unstructured Data

Telfer's change index

Description

Telfers change index is designed to assess the relative change in range size of species between two time periods (Telfer et al 2002). This function can take multiple time periods and will complete all pairwise comparisons.

Usage

telfer(
  taxa,
  site,
  time_period,
  minSite = 5,
  useIterations = TRUE,
  iterations = 10
)

Arguments

taxa	A character vector of taxon names
site	A character vector of site names
time_period	A numeric vector of user defined time periods, or a date vector
minSite	The minimum number of sites occupied in the first time period in order for a trend to be calculated for a taxon.
useIterations	A logical variable indicating whether iterations should be used. Iterations are used to account for increased variation in the logit proportions close to zero and one (see Telfer et al 2002). Default is TRUE
iterations	If useIterations is TRUE, then this parameter indicates the number of iterations to be used. In Telfer et al 2002 the number of iterations used were 7 and 8 for the two datasets for which it was applied. The defualt here is 10.

References

Telfer, M.G., Preston, C.D., & Rothery, P. (2002) A general method for measuring relative change in range size from biological atlas data. Biological Conservation, 107, 99-109.

Examples

# Create fake data
SS <- 5000 # number of observations
taxa <- sample(letters, SS, replace = TRUE)
site <- sample(paste('A', 1:20, sep = ''), SS, replace = TRUE)
time_period <- sample(1:3, SS, replace = TRUE)

TelferResult <- telfer(taxa, site, time_period)
head(TelferResult)

BiologicalRecordsCentre/sparta documentation built on April 22, 2024, 2:34 p.m.