When Alpha Disappears: A One-Switch Benchmark for Decision-Time Leakage in Financial Backtests
We introduce When Alpha Disappears, a paired evaluation benchmark for diagnosing decision-time leakage in financial machine-learning backtests. Rather than treating leakage as a binary property, the benchmark estimates protocol-induced inflation by toggling one evaluation convention at a time around a clean $t{+}1$-open reference, while holding the data panel, walk-forward split, model family, horizon, portfolio rule…