backtest-bias

Survivorship and data-integrity checks for financial price panels, built on measured constants rather than folklore. Measured and published: 24% of India's 2015 top-500 is invisible to free data; 25.7% of the 2010 S&P 500 (20.1% for 2015); a survivor filter moves a US backtest +0.4 to +1.0 pp/yr, and four recycled tickers moved it 1.7 pp/yr, more than the bias itself. One-line checks for survivorship holes, ticker recycling, and universe construction. Audience: retail quants who cannot afford institutional survivorship-free data, which in India is nearly everyone who backtests. Everything public and git-timestamped: PyPI (backtest-bias), a public ledger of 143 failed strategies, SSRN paper 7099378, Kaggle dataset + notebook, weekly write-ups.