secr (version 2.9.0)

secr.test: Goodness-of-Fit Test

Description

Simple Monte-Carlo goodness-of-fit tests for full-likelihood SECR models. The approach is to calculate a statistic from either the raw data or a fitted model, and to relate this to the distribution of the statistic under the original fitted model. The distribution is estimated by simulating data from the model, and possibly re-fitting the model to each simulated dataset. The suitability of different test statistics has yet to be assessed.

Usage

secr.test(object, nsim = 99, statfn, fit = FALSE, seed =
NULL, ncores = 1, tracelevel = 1)

Arguments

object

a fitted secr model

nsim

integer number of replicates

statfn

function to compute a numeric vector of one or more statistics from a single-session `capthist' object or from a fitted model (see Details)

fit

logical; if TRUE the model is re-fitted to each simulated dataset

seed

value for setting .Random.seed - either NULL or an integer

ncores

integer number of cores available for parallel processing

tracelevel

see sim.secr

Value

• An object of class c('secrtest','list') with components:
• object
  as input
• nsim
  as input
• statfn
  as input
• fit
  as input
• seed
  as input
• output
  list comprising the simulated values, the observed value(s), and estimated probabilities
• For multi-session input when fit = FALSE, `output' is a list in which each session provides one component. Print and plot methods are provided for `secrtest' objects.

Details

The test statistic(s) may be computed either on a dataset or on a fitted model, as determined by the argument fit. The single argument expected by statfn should be either a `capthist' object (fit = FALSE) or an `secr' object (fit = TRUE). The default statistic when fit = FALSE is the proportion of individuals observed on only one occasion, which is equivalent to statfn = function(CH) c(f1 = sum(apply(abs(CH) > 0,1,sum) == 1) / nrow(CH)). Repeat detections on one occasion at the same or different detectors are not counted. The default statistic is therefore not appropriate for some data, specifically from `count' or `polygon' detectors with few occasions or only one. The default statistic when fit = TRUE is the deviance divided by the residual degrees of freedom (i.e., statfn = function(object) c(devdf = deviance(object) / df.residual(object))). The reported probability (p) is the rank of the observed value in the vector combining the observed value and simulated values, divided by (nsim + 1). Ranks are computed with rank using the default ties.method = "average". Simulations take account of the usage attribute of detectors in the original capthist object, given that usage was defined and ignoreusage was not set. statfn may return a vector of statistics for each observed or simulated dataset or model: then the value of each statistic will be calculated for every simulated dataset, and summarised. If fit = TRUE the vector of statistics may include both those computed on the raw data (object$capthist) and the fitted model.

See Also

print.secrtest, plot.secrtest, simulate.secr, sim.secr, deviance.secr

Examples

secr.test(secrdemo.0, nsim = 99)

secr.test(ovenbird.model.1, nsim = 20)

## example combining raw data summary and model fit
## assumes single-session
bothfn <- function(object) {
    CH <- object$capthist
    f1 <- sum(apply(abs(CH) > 0, 1, sum) == 1) / nrow(CH)
    devdf <- deviance(object) / df.residual(object)
    c(f1 = f1, devdf = devdf)
}
test <- secr.test (secrdemo.0, nsim = 19, statfn = bothfn, fit = TRUE)
test
plot(test, main = '')