hdrlevels: Highest Density Region (HDR) Levels

In mclust: Gaussian Mixture Modelling for Model-Based Clustering, Classification, and Density Estimation

Highest Density Region (HDR) Levels

Description

Compute the levels of Highest Density Regions (HDRs) for any density and probability levels.

Usage

hdrlevels(density, prob)

Arguments

density	A vector of density values computed on a set of (observed) evaluation points.
prob	A vector of probability levels in the range [0,1].

Details

From Hyndman (1996), let f(x) be the density function of a random variable X. Then the 100(1-\alpha)\% HDR is the subset R(f_\alpha) of the sample space of X such that

R(f_\alpha) = {x : f(x) \ge f_\alpha }

where f_\alpha is the largest constant such that Pr( X \in R(f_\alpha)) \ge 1-\alpha

Value

The function returns a vector of density values corresponding to HDRs at given probability levels.

Author(s)

L. Scrucca

References

Rob J. Hyndman (1996) Computing and Graphing Highest Density Regions. The American Statistician, 50(2):120-126.

See Also

plot.densityMclust

Examples

# Example: univariate Gaussian
x <- rnorm(1000)
f <- dnorm(x)
a <- c(0.5, 0.25, 0.1)
(f_a <- hdrlevels(f, prob = 1-a))

plot(x, f)
abline(h = f_a, lty = 2)
text(max(x), f_a, labels = paste0("f_", a), pos = 3)

mean(f > f_a[1])
range(x[which(f > f_a[1])])
qnorm(1-a[1]/2)

mean(f > f_a[2])
range(x[which(f > f_a[2])])
qnorm(1-a[2]/2)

mean(f > f_a[3])
range(x[which(f > f_a[3])])
qnorm(1-a[3]/2)

# Example 2: univariate Gaussian mixture
set.seed(1)
cl <- sample(1:2, size = 1000, prob = c(0.7, 0.3), replace = TRUE)
x <- ifelse(cl == 1, 
            rnorm(1000, mean = 0, sd = 1),
            rnorm(1000, mean = 4, sd = 1))
f <- 0.7*dnorm(x, mean = 0, sd = 1) + 0.3*dnorm(x, mean = 4, sd = 1)

a <- 0.25
(f_a <- hdrlevels(f, prob = 1-a))

plot(x, f)
abline(h = f_a, lty = 2)
text(max(x), f_a, labels = paste0("f_", a), pos = 3)

mean(f > f_a)

# find the regions of HDR
ord <- order(x)
f <- f[ord]
x <- x[ord]
x_a <- x[f > f_a]
j <- which.max(diff(x_a))
region1 <- x_a[c(1,j)]
region2 <- x_a[c(j+1,length(x_a))]
plot(x, f, type = "l")
abline(h = f_a, lty = 2)
abline(v = region1, lty = 3, col = 2)
abline(v = region2, lty = 3, col = 3)

mclust documentation built on May 29, 2024, 8:06 a.m.