Leave-One-Out Leverage Explorer
Gamma–Poisson conjugate model · prior: λ ~ Gamma(α₀, α₀/5) · 2 000 posterior draws
STAT 418 · §5.7
observed species counts (n = 15 total)
coral ▲ = focus observation y₀
Focus count y₀
5
background mean = 5.0 · range 3–8 · drag toward 20–25 to see LOO fail
Prior strength α₀
4
prior mean = 5.0 · prior SD ≈ 2.50 (weak)
Posterior distribution of λ
— full (n=15)
– – loo (n=14)
dashed lines = posterior means
Importance weights (2 000 draws, sorted)
Uniform = reliable LOO · Spiky = LOO breaks down
μ full
5.000
μ loo
5.000
|Δμ| shift
0.000
ESS / 2000
2000
Pareto-k̂ diagnostic
0.000
0 · good
0.5 · ok
0.7 · bad
1.0 · very bad
1.5+