Ah, so I switch y with x, give it x, and ask it for y (which is actually x). Clever.
I continue to be impressed with R. Thanks, Larry On Friday June 2 2006 11:23, Gabor Grothendieck wrote: > Try this: > > approx(p[,"lwr"], 1:5, 3) > > On 6/2/06, Larry Howe <[EMAIL PROTECTED]> wrote: > > Hello, > > > > Is there a way for R to determine the point where a confidence interval > > equals a specified value? For example: > > > > x = seq(1:5) > > y = c(5, 5, 4, 4, 3) > > lm = lm(y ~ x) > > p = predict.lm(lm, interval="confidence") > > matplot(p, type="b") > > abline(h = 3) > > > > I want to answer the question: "What is the value of x when the y-value > > of the lower confidence interval is equal to 3.0"? Visually, it is the > > place on the example where the abline intersects the lower confidence > > interval, or about 4.2. Can R calculate this number for me? > > > > I know that predict.lm will calculate a y-value from an x-value, but what > > I want is the opposite. I know the y-value, and I want to calculate the > > x-value. > > > > Larry Howe > > > > ______________________________________________ > > R-help@stat.math.ethz.ch mailing list > > https://stat.ethz.ch/mailman/listinfo/r-help > > PLEASE do read the posting guide! > > http://www.R-project.org/posting-guide.html ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
