arXiv:2608.07303cs.AIcs.LG2026-08

短时间预算下AutoML比较易被测试集选择和预算不执行误导,真实表现差距远小于表面数据。

Winning by Peeking: Unenforced Budgets and Test-Set Selection Inflate Short-Budget AutoML Comparisons

  • 在测试集上反复评估候选模型,使结果受噪声影响夸大优势。
  • 实际运行时间超预算2.24倍,且未强制执行,导致虚假性能领先。
  • 调整验证策略与资源分配后,胜率从59.4%降至34.3%,差距不再显著。

在数十秒级短预算下对比AutoML系统极为常见,但极易出错。我们发现一个简单引擎Orcetra看似在513个OpenML数据集上以60秒预算击败FLAML和AutoGluon,胜率达57.1%,对FLAML更达78.4%。然而这些优势源于协议缺陷:搜索循环在测试集上多次评分并报告最高值,而基线仅在训练集选型且仅接触测试集一次;预算在启动前检查但未执行,导致其平均耗时120秒,是基准的2.24倍。重跑实验中,将选择移至验证集、外部强制预算、公平分配算力后,Orcetra胜率从59.4%降至34.3%,与任一对手差异均不显著。通过统一记录评估指标,我们归因发现:选择规则贡献4.8个百分点,计算不均占其余部分。相同数据揭示选择偏差随 $K$ 增长,但仅达0.27准确率点,远低于理论预测($σ\sqrt{2\ln K}$),因共享测试样本的噪声相互抵消。论文末尾附有短预算比较清单,代码、每数据集结果及复现脚本均已公开。

原文摘要 · Abstract (English)

Comparisons between AutoML systems at short time budgets -- tens of seconds rather than hours -- are common in tool READMEs and workshop papers, and they are easy to get wrong. We report a case study in which a simple AutoML engine, Orcetra, appeared to beat FLAML and AutoGluon on 513 OpenML datasets, winning 57.1% of them at a nominal 60-second budget and 78.4% of datasets against FLAML alone at 30 seconds. Both margins came from protocol defects that a results table cannot show. The search loop scored every candidate on the test split and reported the best, making the headline metric a maximum over dozens of noisy estimates while the baselines selected on training data and touched the test set once; and the budget was checked before launching a candidate but never enforced during one, so the system consumed a median of 120 s against a 60-second budget, 2.24x the wall-clock AutoGluon used. Re-running with selection moved to a validation split, the deadline enforced externally and every framework pinned to an equal share of the machine, Orcetra's win rate on the re-run subset falls from 59.4% to 34.3% and no pairwise difference against either competitor remains significant. Recording both estimands inside a single search lets us attribute the collapse: the selection rule accounts for 4.8 percentage points and unequal compute for most of the rest. The same traces give the selection bias as a function of budget, measured rather than assumed: it grows with $K$ but reaches only 0.27 accuracy points, about five times below the $σ\sqrt{2\ln K}$ bound a marginal-standard-error argument predicts, because candidates scored on shared test rows cancel most of the noise. We close with a checklist for short-budget comparisons. Code, per-dataset results and the scripts that regenerate every number and figure in the paper are released with it.

AutoML实验偏差测试集污染基准测试

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