Date: 2025-11-21

# Confidence Functionals for SelectBoost-GAMLSS

#### Frédéric Bertrand

#### 2025-11-21

We consider stability curves \(p_j(c0)\) for each term \(j\) across a grid of SelectBoost thresholds `c0`. The following functionals condense these curves into scalar confidences:

## What you’ll learn

- How to compute `confidence_functionals()` from a `sb_gamlss_c0_grid()` result.
- How to plot ranking summaries (`plot()`) and raw stability trajectories (`plot_stability_curves()`).
- How to customise weights, quantiles, and conservative adjustments for different decision rules.

1. AUSC (Area Under the Stability Curve): normalized trapezoidal area over the grid.
2. Thresholded AUSC: integrate the positive excess \((p - \pi^\star)_+\).
3. Coverage: fraction of grid points with \(p \ge \pi^\star\).
4. Quantiles: median and high quantiles (e.g., 80th/90th) of \(p\) across `c0`.
5. Weighted AUSC: integrate \(w(c0)\,p(c0)\) normalized by \(\int w(c0)\,dc0\).
6. Conservative AUSC: replace \(p\) by a Wilson lower bound before integrating.

    library(gamlss)
    library(SelectBoost.gamlss)

    set.seed(1)
    n <- 400
    x1 <- rnorm(n); x2 <- rnorm(n); x3 <- rnorm(n)
    y  <- gamlss.dist::rNO(n, mu = 1 + 1.3*x1 - 1.0*x3, sigma = 1)
    dat <- data.frame(y, x1, x2, x3)

    g <- sb_gamlss_c0_grid(
      y ~ 1, data = dat, family = gamlss.dist::NO(),
      mu_scope = ~ x1 + x2 + x3, sigma_scope = ~ x1 + x2,
      c0_grid = seq(0.2, 0.8, by = 0.2), B = 40, pi_thr = 0.6, pre_standardize = TRUE, trace = FALSE
    )
    #>   |                                                                              |                                                                      |   0%  |                                                                              |==================                                                    |  25%  |                                                                              |===================================                                   |  50%
    #> Warning in RS(): Algorithm RS has not yet converged
    #>   |                                                                              |====================================================                  |  75%  |                                                                              |======================================================================| 100%

    cf <- confidence_functionals(
      g, pi_thr = 0.6, q = c(0.5, 0.8, 0.9),
      weight_fun = NULL, conservative = FALSE, method = "trapezoid"
    )

    plot(cf, top = 10, label_top = 6)

    plot_stability_curves(g, terms = c("x1","x3"), parameter = "mu")