通过优化连续概率评分,用分箱法实现更精确的非参数预测分布估计。
CRPS-Optimal Binning for Univariate Conformal Regression
- 按协变量排序数据分箱,用箱内经验累积分布函数作预测分布
- 最小化留一法CRPS选最优分箱数,交叉验证避免过拟合
- 无需预留验证集,预测区间更窄且覆盖率达标,适合高精度场景
我们提出一种基于分箱的非参数条件分布估计方法:将协变量排序后的观测值划分为连续区间,使用箱内经验累积分布函数作为预测分布。箱边界通过最小化总留一法连续概率评分(LOO-CRPS)确定,该成本函数具有 $O(n^2 "log n)$ 的预计算复杂度和 $O(n^2)$ 存储开销;全局最优 $K$-分段可通过动态规划在 $O(n^2 K)$ 时间内求解。但直接最小化样本内 LOO-CRPS 会引入过拟合偏差,因此改用 $K$-折交叉验证测试 CRPS 来选择 $K$,其表现呈典型 U 型曲线并有明确最小值。选定最佳 $K^*$ 后,利用全数据集分箱结果构建两类互补预测对象:Venn 预测带与基于 CRPS 作为非符合性得分的置信集,后者在任意给定水平 $\varepsilon$ 下具备有限样本边际覆盖率保证。该方法为逐次预测,数据利用高效,所有样本同时用于分箱与 $p$-值计算,无需保留独立验证集。在真实基准上,相较于分割式方法(高斯分割合取、CQR、CQR-QRF、校准化保序分布回归),本方法在保持接近名义覆盖率的同时,显著缩小了预测区间。
原文摘要 · Abstract (English)
We propose a method for non-parametric conditional distribution estimation based on partitioning covariate-sorted observations into contiguous bins and using the within-bin empirical CDF as the predictive distribution. Bin boundaries are chosen to minimise the total leave-one-out Continuous Ranked Probability Score (LOO-CRPS), which admits a closed-form cost function with $O(n^2 \log n)$ precomputation and $O(n^2)$ storage; the globally optimal $K$-partition is recovered by a dynamic programme in $O(n^2 K)$ time. Minimisation of within-sample LOO-CRPS turns out to be inappropriate for selecting $K$ as it results in in-sample optimism. We instead select $K$ by $K$-fold cross-validation of test CRPS, which yields a U-shaped criterion with a well-defined minimum. Having selected $K^*$ and fitted the full-data partition, we form two complementary predictive objects: the Venn prediction band and a conformal prediction set based on CRPS as the nonconformity score, which carries a finite-sample marginal coverage guarantee at any prescribed level $\varepsilon$. The conformal prediction is transductive and data-efficient, as all observations are used for both partitioning and p-value calculation, with no need to reserve a hold-out set. On real benchmarks against split-conformal competitors (Gaussian split conformal, CQR, CQR-QRF, and conformalized isotonic distributional regression), the method produces substantially narrower prediction intervals while maintaining near-nominal coverage.
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