timevaryingcov: Time-varying Covariates

In secr: Spatially Explicit Capture-Recapture

Time-varying Covariates

Description

Extract or replace time varying covariates

Usage

timevaryingcov(object, ...)
timevaryingcov(object) <- value

Arguments

object	an object of class traps or capthist
value	a list of named vectors
...	other arguments (not used)

Details

The timevaryingcov attribute is a list of one or more named vectors. Each vector identifies a subset of columns of covariates(object), one for each occasion. If character values are used they should correspond to covariate names.

In secr models, time-varying covariates are restricted to traps objects. Time-varying (session-specific) individual covariates may be used in openCR. The following remarks apply to time-varying traps covariates.

The name of the vector may be used in a model formula; when the model is fitted, the value of the trap covariate on a particular occasion is retrieved from the column indexed by the vector.

For replacement, if object already has a usage attribute, the length of each vector in value must match exactly the number of columns in usage(object).

When converting a multi-session capthist object into a robust-design “single-session” object with function join the argument ‘timevaryingcov’ is used to collate covariate values across sessions in a form suitable for inclusion in openCR models (see join).

Value

timevaryingcov(object) returns the timevaryingcov attribute of object (may be NULL).

Note

It is usually better to model varying effort directly, via the usage attribute (see secr-varyingeffort.pdf).

Models for data from detectors of type ‘multi’, ‘polygonX’ or ‘transectX’ take much longer to fit when detector covariates of any sort are used.

Time-varying covariates are not available with the (default) 'fastproximity' option.

See secr-varyingeffort.pdf for input of detector covariates from a file.

See Also

join

Examples

# make a trapping grid with simple covariates
temptrap <- make.grid(nx = 6, ny = 8, detector = "multi") 
covariates (temptrap) <- data.frame(matrix(
    c(rep(1,48*3),rep(2,48*2)), ncol = 5))
head(covariates (temptrap))

# identify columns 1-5 as daily covariates
timevaryingcov(temptrap) <- list(blockt = 1:5)
timevaryingcov(temptrap)

## Not run: 

# default density = 5/ha, noccasions = 5
CH <- sim.capthist(temptrap, detectpar = list(g0 = c(0.15, 0.15,
    0.15, 0.3, 0.3), sigma = 25))

fit.1 <- secr.fit(CH, trace = FALSE) 
fit.tvc2 <- secr.fit(CH, model = g0 ~ blockt, trace = FALSE) 

# because variation aligns with occasions, we get the same with:
fit.t2 <- secr.fit(CH, model = g0 ~ tcov, timecov = c(1,1,1,2,2),
    trace = FALSE) 

predict(fit.t2, newdata = data.frame(tcov = 1:2))
predict(fit.tvc2, newdata = data.frame(blockt = 1:2))

# now model some more messy variation
covariates (traps(CH))[1:10,] <- 3
fit.tvc3 <- secr.fit(CH, model = g0 ~ blockt, trace = FALSE) 

AIC(fit.tvc2, fit.t2, fit.tvc3)
# fit.tvc3 is the 'wrong' model


## End(Not run)

secr documentation built on Nov. 4, 2024, 9:06 a.m.