bmd <- read.delim("../../data/bmd.txt")
require(mgcv)
fit <- gam(spnbmd~s(age,by=gender),data=bmd)
summary(fit)

fit0 <- gam(spnbmd~gender*age,data=bmd)
anova(fit0,fit,test="F")

fit <- gam(spnbmd~s(age),data=bmd)
fit0 <- gam(spnbmd~age,data=bmd)
anova(fit0,fit,test="F")

fit <- gam(spnbmd~s(age),data=bmd)
fit0 <- gam(spnbmd~1,data=bmd)
anova(fit0,fit2,test="F")
summary(fit)

fit <- gam(spnbmd~s(age,by=gender),data=bmd)
par(mfrow=c(1,2))
plot(fit,shade=TRUE)