eva {lax}

Loglikelihood adjustment for eva fits

Description

S3 alogLik method to perform loglikelihood adjustment for fitted extreme value model objects returned from the functions gevrFit and gpdFit in the eva package.

Usage

## S3 method for class 'gevrFit'
alogLik(x, cluster = NULL, use_vcov = TRUE, ...)

## S3 method for class 'gpdFit'
alogLik(x, cluster = NULL, use_vcov = TRUE, ...)

Arguments

x

A fitted model object with certain associated S3 methods. See Details.

cluster

A vector or factor indicating from which cluster the respective log-likelihood contributions from loglik originate. The length of cluster must be consistent with the estfun method to be used in the estimation of the 'meat' V of the sandwich estimator of the covariance matrix of the parameters to be passed to adjust_loglik. In most cases, cluster must have length equal to the number of observations in data. The exception is the GP (only) model (binom = FALSE), where the cluster may either contain a value for each observation in the raw data, or for each threshold exceedance in the data.

If cluster is not supplied (is NULL) then it is assumed that each observation forms its own cluster. See Details for further details.

use_vcov

A logical scalar. Should we use the vcov S3 method for x (if this exists) to estimate the Hessian of the independence loglikelihood to be passed as the argument H to adjust_loglik? Otherwise, H is estimated inside adjust_loglik using optimHess.

...

Further arguments to be passed to the functions in the sandwich package meat (if cluster = NULL), or meatCL (if cluster is not NULL).

Details

See alogLik for details.

In the stationary case (no covariates) the function gevrFit and gpdFit in the eva package offer standard errors based on the expected information or on the observed information, via the argument information. In contrast, alogLik() always bases calculations on the observed information matrix. Therefore, unadjusted standard errors resulting from alogLik() may be different the corresponding standard errors from gevrFit or gpdFit.

For gevrFit only GEV fits (gumbel = FALSE) are supported.

Value

An object inheriting from class "chandwich". See adjust_loglik. class(x) is a vector of length 5. The first 3 components are c("lax", "chandwich", "eva"). The 4th component depends on which model was fitted. "rlarg" if gevrFit was used; "gpd" if gpdFit was used. The 5th component is "stat" if there are no covariates in the mode and "nonstat" otherwise.

References

Chandler, R. E. and Bate, S. (2007). Inference for clustered data using the independence loglikelihood. Biometrika, 94(1), 167-183. doi:10.1093/biomet/asm015

Suveges, M. and Davison, A. C. (2010) Model misspecification in peaks over threshold analysis, The Annals of Applied Statistics, 4(1), 203-221. doi:10.1214/09-AOAS292

Zeileis (2006) Object-Oriented Computation and Sandwich Estimators. Journal of Statistical Software, 16, 1-16. doi:10.18637/jss.v016.i09

See Also

alogLik: loglikelihood adjustment for model fits.

Examples

# We need the eva package
got_eva <- requireNamespace("eva", quietly = TRUE)

if (got_eva) {
  library(eva)
  # An example from the eva::gpdFit documentation
  set.seed(7)
  x <- eva::rgpd(2000, loc = 0, scale = 2, shape = 0.2)
  mle_fit <- eva::gpdFit(x, threshold = 4, method = "mle")
  adj_mle_fit <- alogLik(mle_fit)
  summary(adj_mle_fit)

  # Another example from the eva::gpdFit documentation
  # A linear trend in the scale parameter
  set.seed(7)
  n <- 300
  x2 <- eva::rgpd(n, loc = 0, scale = 1 + 1:n / 200, shape = 0)
  covs <- as.data.frame(seq(1, n, 1))
  names(covs) <- c("Trend1")
  result1 <- eva::gpdFit(x2, threshold = 0, scalevars = covs,
                         scaleform = ~ Trend1)
  adj_result1 <- alogLik(result1)
  summary(adj_result1)

  # An example from the eva::gevrFit documentation
  set.seed(7)
  x1 <- eva::rgevr(500, 1, loc = 0.5, scale = 1, shape = 0.3)
  result1 <- eva::gevrFit(x1, method = "mle")
  adj_result1 <- alogLik(result1)
  summary(adj_result1)

  # Another example from the eva::gevrFit documentation
  # A linear trend in the location and scale parameter
  n <- 100
  r <- 10
  x2 <- eva::rgevr(n, r, loc = 100 + 1:n / 50,  scale = 1 + 1:n / 300,
                   shape = 0)
  covs <- as.data.frame(seq(1, n, 1))
  names(covs) <- c("Trend1")
  # Create some unrelated covariates
  covs$Trend2 <- rnorm(n)
  covs$Trend3 <- 30 * runif(n)
  result2 <- eva::gevrFit(data = x2, method = "mle", locvars = covs,
                          locform = ~ Trend1 + Trend2*Trend3,
                          scalevars = covs, scaleform = ~ Trend1)
  adj_result2 <- alogLik(result2)
  summary(adj_result2)
}