mev (version 1.11)

egp: Extended generalised Pareto families

Description

This function provides the log-likelihood and quantiles for the three different families presented in Papastathopoulos and Tawn (2013). The latter include an additional parameter, \(\kappa\). All three families share the same tail index than the GP model, while allowing for lower thresholds. In the case \(\kappa=1\), the models reduce to the generalised Pareto.

egp.retlev gives the return levels for the extended generalised Pareto distributions

Arguments

xdat

vector of observations, greater than the threshold

thresh

threshold value

par

parameter vector (\(\kappa\), \(\sigma\),\(\xi\)).

model

a string indicating which extended family to fit

p

extreme event probability; p must be greater than the rate of exceedance for the calculation to make sense. See Details.

plot

boolean indicating whether or not to plot the return levels

Value

egp.ll returns the log-likelihood value.

egp.retlev returns a plot of the return levels if plot=TRUE and a matrix of return levels.

Usage

egp.ll(xdat, thresh, par, model=c("egp1","egp2","egp3"))

egp.retlev(xdat, thresh, par, model=c("egp1","egp2","egp3"), p, plot=TRUE)

Details

For return levels, the p argument can be related to \(T\) year exceedances as follows: if there are \(n_y\) observations per year, than take p to equal \(1/(Tn_y)\) to obtain the \(T\)-years return level.

References

Papastathopoulos, I. and J. Tawn (2013). Extended generalised Pareto models for tail estimation, Journal of Statistical Planning and Inference 143(3), 131--143.

Examples

# NOT RUN {
set.seed(123)
xdat <- evd::rgpd(1000, loc=0, scale=1, shape=0.5)
par <- egp.fit(xdat, thresh=0, model="egp3")$par
p <- c(1/1000,1/1500,1/2000)
egp.retlev(xdat, 0, par, "egp3",p)
#With multiple thresholds
th <- c(0,0.1,0.2,1)
opt <- egp.fitrange(xdat, th, model="egp1",plots=NA)
egp.retlev(xdat, opt$thresh, opt$par, "egp1",p=p)
opt <- egp.fitrange(xdat, th, model="egp2",plots=NA)
egp.retlev(xdat, opt$thresh, opt$par, "egp2",p=p)
opt <- egp.fitrange(xdat, th, model="egp3",plots=NA)
egp.retlev(xdat, opt$thresh, opt$par, "egp3",p=p)
# }