We present a conservative robustness assessment of weak dipole fits in the Pantheon+ Type Ia supernova sample. The analysis is motivated by previous studies that reported moderate indications of directional dependence in the supernova distance–redshift relation, including a previously proposed dipole analysis of Pantheon+. Rather than introducing a new cosmological model or claiming a detection of anisotropy, we examine how the fitted dipole amplitude and direction respond to controlled changes in the analysis pipeline. Starting from a replication of a previously proposed Pantheon+ dipole fit, we apply a structured set of robustness tests involving redshift cuts, redshift-frame definitions, an operational treatment of peculiar velocities, leave-one-survey-out jackknife tests, hemispherical partitions, and declination-selection checks. All tests use the same underlying Pantheon+ data release and covariance structure, with each block interpreted relative to a predefined reference configuration. We find that the background cosmological parameters remain comparatively stable across the tests, while the fitted dipole component is more sensitive to methodological choices. In particular, the recovered amplitude and direction depend appreciably on the redshift definition, the operational treatment of peculiar velocities, the low-redshift regime, and the effective angular coverage of the sample. These results indicate that the Pantheon+ dipole fit should not be interpreted, by itself, as a strongly methodologically robust detection of cosmological anisotropy. The main contribution of this work is a reproducible framework for distinguishing between structurally stable directional features and fitted dipole components whose characterization depends on analysis choices in Type Ia supernova samples.This record includes the manuscript PDF and a supplementary CSV master table containing the dipole-fit results used in the robustness assessment.
Miguel Viso Cervera (Sun,) studied this question.