{
  "id": 14195163,
  "title": "Overlapping windows will manufacture statistical significance in your backtest",
  "url": "https://urgent.news/2026/10/13/overlapping-windows-will-manufacture-statistical-significance-in-your",
  "topic": "tech",
  "section": "Tech",
  "published": "2026-10-13T12:10:02.000Z",
  "source": {
    "name": "Dev.to",
    "slug": "dev-to",
    "url": "https://dev.to/michaelhairetis/overlapping-windows-will-manufacture-statistical-significance-in-your-backtest-jjj"
  },
  "original_language": "en",
  "account": "A walk-forward test with 913 causal anchors and a 30-minute forecast horizon produced a misleading 55.2% accuracy result, nearly doubling from the actual 51.1% majority class. This occurred due to overlapping windows, where test points shared 23 out of their 30 minutes of outcome. The inflated sample size of 912 was actually a smaller number of distinct market episodes counted repeatedly, leading to artificially small error bars. Re-testing on non-overlapping anchors reduced the sample size to 163, increasing the edge to +5.5 pp with smaller standard errors. The key trap is that larger effect sizes can be misleading, making noise appear as a stronger real effect. To avoid this, compare anchor spacing to the forecast horizon and either re-score on non-overlapping anchors or space them a full horizon apart. This issue applies to any sliding-window evaluation where the window is wider than the stride, including sensor data, load forecasting, anomaly detection, and medical monitoring.",
  "summary": "The easiest way to publish a false positive in time-series work, with a worked example from my own project. The result that looked publishable A walk-forward test, 913 causal anchors, direction accuracy at a 30-minute horizon. Benchmark note that matters: the thing to beat is not 50%, it is the majority class . If 51% of moves were up, \"always guess up\" scores 51%. Scoring against 50% is how a…",
  "key_points": [],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}