Parity Asymmetry at Low Multipoles: The Strongest Odd-Even Imbalance Cosmic Variance Permits, and Where the Reported Effect Sits Within It

Point-parity asymmetry, an excess of power in odd multipoles over even ones at large angles, has been reported in the microwave sky at up to roughly three-sigma significance in some treatments. This paper computes the exact null behaviour of the standard parity ratio by Monte Carlo over the known chi-square distribution of power estimates. Summing to multipole 20, the ratio's median is 1.04, its fifth percentile is 0.822, its first percentile 0.745, and a ratio of 0.85, representative of the reported effect, falls at the 7.91 percentile. The reported asymmetry is thus a roughly two-sigma class fluctuation of a statistic with a wide, skewed null distribution, and reaching the first percentile would require a ratio of 0.745. Because neighbouring choices of the maximum multipole give similar percentiles, the effect is stable but modest: parity is a statistic in which the sky looks mildly unusual from every angle and decisive from none. The study is simulated, not measured.