pondfrog: Fake Data of the Numbers of Frogs in Ponds
Description
The data contain frog population sizes in different ponds with some characteristics of ponds.
The data is simulated, thus the "true" model is known. The data can serve to play with
different methods for doing model selection.
Usage
data(pondfrog)
Arguments
Details
The r-code for producing the pondfrog data is
set.seed(196453)
n <- 130 # sample size
height <- sample(150:1500,n)
region <- sample(c("south", "north"), n, replace=TRUE, prob=c(0.2, 0.8))
waterdepth <- sample(seq(0.3, 5.5, by=0.01), n)
surfacearea <- sample(seq(3, 150), n)
temp <- 20 - 0.01*height + 0.5*as.numeric(region=="south") -0.005*waterdepth + 0.1*sqrt(surfacearea) +rnorm(n, 0, 1.5)
ph <- 7.5 - 0.8 * as.numeric(region=="south") + rnorm(n, 0, 0.2)
vegdensity.logitp <- -3.5+0.3*ph + 0.2*temp+rnorm(n,0,1)
vegdensity.p <- plogis(vegdensity.logitp)
vegdensity <- rbinom(n, 1, prob=vegdensity.p)
fish.logitp <- -4+0.3*ph + 0.2*waterdepth+rnorm(n,0,1)
fish.p <- plogis(fish.logitp)
fish <- rbinom(n, 1, prob=fish.p)
frog.mu <- exp(3.5 + 0.2*(temp-mean(temp)) +0.2*(ph-mean(ph)) + 0.1*(ph-mean(ph))^2 -
0.3*(waterdepth-mean(waterdepth)) - 0.5 * fish + 0.5*fish*vegdensity)
frog <- rpois(n, lambda=frog.mu)
dat <- data.frame(frog=frog, fish=fish, vegdensity=vegdensity, ph=ph, surfacearea=surfacearea,
waterdepth=waterdepth, region=region, height=height, temp=temp)
Thus, the "true" model for the number of pondfrog (frog) is a Poisson model
with log-link function and the following linear predictor:
3.5 + 0.2*(temp-mean(temp)) +0.2*(ph-mean(ph)) + 0.1*(ph-mean(ph))^2 -
0.3*(waterdepth-mean(waterdepth)) - 0.5 * fish + 0.5*fish*vegdensity