# Tag Info

The calculation is described in the IEX Rule Book, section 11.160 (g). See Quote Instability Factor (QFI) and the accompanying thresholds: $$QIF = \frac{1}{1+e^{-x}}$$ where $$x = C_0 + C_1N + C_2F + C_3NC + C_4FC + C_5EPos+C_6ENeg+C_7 EPosPrev+C_8ENegPrev + C_9Delta$$ The coefficients $C_n$ are hard-coded and are updated once in a while with a ...