Anisotropic Stability in High-Redshift Quasar Distributions: A Double-Blind and Agnostic Cosmography Audit of SDSS DR16Q

The assumption of large-scale statistical isotropy remains a foundational pillar of the ΛCDM cosmological model. However,persistent tensions across independent probes suggest potential limitations in the Friedmann-Lemaˆıtre-Robertson-Walker(FLRW) metric. We present a comprehensive, model-independent audit of directional anisotropy in the Sloan Digital SkySurvey Data Release 16 Quasar catalog (SDSS DR16Q). To eliminate the circularity inherent in standard ΛCDM detrendingpipelines—which often absorb transversal variance into intrinsic error dispersion—we employ an agnostic cosmographicbaseline using high-order Taylor and Pad´e kinematic expansions. Analyzing N = 216,410 quasars in the deep vacuumstratum (1.5 ≤ z ≤ 2.0) with a strict Galactic latitude cut (|b| > 20◦), we investigate a dipolar modulation exhibiting aredshift-dependent precession. By fixing the kinematic precession prior (ωp ≈ 18.08 rad/z) derived from the independentPantheon+ supernova sample, we strictly constrain our degrees of freedom and mitigate the look-elsewhere effect. Followingan orthogonal multiple regression cleaning that removed 9.18% of SDSS observational variance, the transversal signal yieldsa Z-score significance of 16.25σ. A 100-fold split-half cross-validation protocol yields a median detection of 8.60σ on completely unseen data, ruling out algorithmic overfitting and confirming structural stability. The detected purified precessionalaxis (ϕ0 = 174.0◦) is consistent with reported CMB low-multipole anomalies, establishing a robust observational tensionwith the premise of perfect statistical isotropy