Example Exponential distribution
Test H0 : θ = θ0 against H1 : θ>θ0.
Here Θ0 = {θ0}, Θ1 = [θ0,∞).
The likelihood function is
L(θ; x) = n
i=1
f(xi; θ) = θne−θ
xi .
The numerator of the likelihood ratio is
L(θ0; x) = θn
0 e−nθ0x.
We need to find the supremum as θ ranges over the interval [θ0,∞). Now
l(θ; x) = n log θ − nθx
so that
∂l(θ;x)
∂θ = n
θ − nx
which is zero only when θ =1/x. Since L(θ; x) is an increasing function for
θ < 1 /x and decreasing for θ > 1 /x,
sup {L(θ;x) : θ ∈ Θ} =
x−ne−n, if 1 /x ≥ θ0
θn
0 e−nθ0x