My GAM curves are being shifted downwards. Is there something wrong with the intercept? I'm using the same code as Introduction to statistical learning
... Any help's appreciated..
Here's the code. I simulated some data (a straight line with noise), and fit GAM multiple times using bootstrap. (It took me a while to figure out how to plot multiple GAM fits in one graph. Thanks to this post Sam's answer, and this post)
library(gam)
N = 1e2
set.seed(123)
dat = data.frame(x = 1:N,
y = seq(0, 5, length = N) + rnorm(N, mean = 0, sd = 2))
plot(dat$x, dat$y, xlim = c(1,100), ylim = c(-5,10))
gamFit = vector('list', 5)
for (ii in 1:5){
ind = sample(1:N, N, replace = T) #bootstrap
gamFit[[ii]] = gam(y ~ s(x, 10), data = dat, subset = ind)
par(new=T)
plot(gamFit[[ii]], col = 'blue',
xlim = c(1,100), ylim = c(-5,10),
axes = F, xlab='', ylab='')
}