CODEWITHSUNDEEP
rplot
student_t
student_t

Reputation: 243

R: Plotting Confidence Bands Issue

I am trying to plot confidence bands for a regression, using a function but the lines for my upper and lower prediction bands look weird and blurry. Can anyone spot the issue, because I can't seem to find anything wrong?

Here is the code: 

drawPrediction <- function(x, y) {

  lm.model <- lm(y ~ x)
  ci <- predict(lm.model, interval = "prediction")
  plot(x,y)
  abline(lm.model, col = "red")
  lines(x, ci[,2], lty = 2, col = 'blue')
  lines(x,ci[,3], lty = 2, col = 'blue' )

}

Gives this result for some test data (the R state.x77 data, regressing Income on Illiteracy):

enter image description here

This is the code I used for the test above:

> test <- as.data.frame(state.x77)
> drawPrediction(test$Illiteracy, test$Income)

Upvotes: 1

Views: 1290

Answers (1)

G5W
G5W

Reputation: 37641

The problem is that the x's are not sorted so you are drawing lines all over the place, not just between consecutive x's. Instead, use

lm.model <- lm(Income ~ Illiteracy, data=as.data.frame(state.x77))
  ci <- predict(lm.model, interval = "prediction")
  plot(x,y)
  abline(lm.model, col = "red")
  lines(sort(x), ci[order(x),2], lty = 2, col = 'blue')
  lines(sort(x), ci[order(x),3], lty = 2, col = 'blue' )

Sorted x's

Upvotes: 3

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