Conditionally colour data points outside of confidence bands in R

Question

I need to colour datapoints that are outside of the the confidence bands on the plot below differently from those within the bands. Should I add a separate column to my dataset

Answer 1

I liked the idea and tried to make a function for that. Of course it's far from being perfect. Your comments are welcome

diseasesev<-c(1.9,3.1,3.3,4.8,5.3,6.1,6.4,7.6,9.8,12.4)
# Predictor variable, (Centigrade)
temperature<-c(2,1,5,5,20,20,23,10,30,25)

## For convenience, the data may be formatted into a dataframe
severity <- as.data.frame(cbind(diseasesev,temperature))

## Fit a linear model for the data and summarize the output from function lm()
severity.lm <- lm(diseasesev~temperature,data=severity)

# Function to plot the linear regression and overlay the confidence intervals   
ci.lines<-function(model,conf= .95 ,interval = "confidence"){
  x <- model[[12]][[2]]
  y <- model[[12]][[1]]
  xm<-mean(x)
  n<-length(x)
  ssx<- sum((x - mean(x))^2)
  s.t<- qt(1-(1-conf)/2,(n-2))
  xv<-seq(min(x),max(x),(max(x) - min(x))/100)
  yv<- coef(model)[1]+coef(model)[2]*xv

  se <- switch(interval,
        confidence = summary(model)[[6]] * sqrt(1/n+(xv-xm)^2/ssx),
        prediction = summary(model)[[6]] * sqrt(1+1/n+(xv-xm)^2/ssx)
              )
  # summary(model)[[6]] = 'sigma'

  ci<-s.t*se
  uyv<-yv+ci
  lyv<-yv-ci
  limits1 <- min(c(x,y))
  limits2 <- max(c(x,y))

  predictions <- predict(model, level = conf, interval = interval)

  insideCI <- predictions[,'lwr'] < y & y < predictions[,'upr']

  x_name <- rownames(attr(model[[11]],"factors"))[2]
  y_name <- rownames(attr(model[[11]],"factors"))[1]

  plot(x[insideCI],y[insideCI],
  pch=16,pty="s",xlim=c(limits1,limits2),ylim=c(limits1,limits2),
  xlab=x_name,
  ylab=y_name,
  main=paste("Graph of ", y_name, " vs ", x_name,sep=""))

  abline(model)

  points(x[!insideCI],y[!insideCI], pch = 16, col = 'red')

  lines(xv,uyv,lty=2,col=3)
  lines(xv,lyv,lty=2,col=3)
}

Use it like this:

ci.lines(severity.lm, conf= .95 , interval = "confidence")
ci.lines(severity.lm, conf= .85 , interval = "prediction")