Follow-up: [R] Inverse prediction with R?
wsi at gcal.ac.uk
Tue Feb 22 15:18:19 CET 2000
y = a+b*x
Then you get the inverse regression estimate
x = (y-a)/b
I don't see what is hard about that.
As for the confidence interval for x, try bootstrapping:
- randomly sample your (x,y) data
- do the y = a+b*x fit
- get the estimate x = (y-a)/b
- use the bootstrapped x distribution to get your CI
Or use the formulas you saw in a book.
I don't see this as a hard programming project. (I am no ace R programmer
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