three_term_model <- gam(y~x0+s(x1)+s(x2)+x3, data=gam_data)
three_smooth_model <- gam(y~x0+s(x1)+s(x2)+s(x3), data=gam_data)
three_smooth_summary <- summary(three_smooth_model)

print(three_smooth_summary$p.table)
print(three_smooth_summary$s.table)
plot(three_smooth_model,page=1)
# edf = 1 therefore term is linear.

anova(two_smooth_model,three_term_model,test="Chisq")
# term x3 is not significant