[R] Finding points with equal probability between normal distributions

[Uwe Ligges]

Eleni Rapsomaniki wrote:
> Dear mailing list, 
> 
> For two normal distributions, e.g:
> 
> r1 =rnorm(20,5.2,2.1)
> r2 =rnorm(20,4.2,1.1)
> plot(density(r2), col="blue")
> lines(density(r1), col="red")


dr1 <- density(r1, from=-3, to=14)
dr2 <- density(r2, from=-3, to=14)
w <- which(diff(sign(dr2$y -  dr1$y)) != 0)
dr1$x[w]

plot(dr1, ylim = c(0, 0.33))
lines(dr2, col = "red")
abline(v = dr1$x[w], col = "blue")

Uwe Ligges



> Is there a way in R to compute/estimate the point(s) x where the density of the
> two distributions cross (ie where x has equal probability of belonging to
> either of the two distributions)?
> 
> Many Thanks
> 
> Eleni Rapsomaniki
> PhD student
> Birkbeck College, UK
> 
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