# Fitting a broken stick regression with confidence intervals

I have been trying to fit a scatter plot of a broken stick regression with confidence intervals. What I would like is to have two different regression lines and confidence intervals between the inflection point. I've already determined the inflection point using the SiZer package. I have tried to plot this two ways, by trying to graph 2 scatter plots (of the data groups based on the inflection point) with regressions and CIs on one graph, and also by indicating the inflection point (Tb>33.688) in the code, but have just received errors. I would like a graph similar to this, but with 2 different regression lines and CIs around the significant inflection point at 33.688

   p<-ggplot (thermalb, aes(x=thermalb$$Ta, y=thermalb$$Tb))+
geom_point (color= "#69b3a2")+
xlab("Air temperature (°C)")+
ylab("Body temperature(°C)")+
geom_smooth(method=lm , color="red", se=TRUE)


You need to categorize your observations according to the changepoint, and pass it as group in ggplot, for example:

library(SiZer)
library(ggplot2)
data(Arkansas)
dat = Arkansas
model <- piecewise.linear(dat$$year,dat$$sqrt.mayflies, CI=FALSE)
#group according to the changepoint
dat$$grp = factor(ifelse(Arkansas$$year > model\$change.point,1,0))

ggplot(dat,aes(x=year,y=sqrt.mayflies,group=grp)) +
geom_point() + geom_smooth(method="lm",formula=y~x,col="red")