Data feeds and backtests: bad data can create fake confidence

Historical data quality matters because a backtest is only as good as the inputs. Missing ticks, adjusted prices, wrong timestamps, and survivorship bias can all create misleading results. Before trusting any strategy test, I would check the source, cleaning process, and whether the same logic still works on unseen data.

Inspired by public discussion themes on EliteTrader new posts, rewritten as original InvestForum discussion content: https://www.elitetrader.com/et/whats-new/posts/