Morphology–ADF Statistical Association in Planetary Nebulae (Revised Pilot Study)

This work presents a revised pilot study investigating the statistical relationship between nebular morphology and the Abundance Discrepancy Factor (ADF) in planetary nebulae. Using manually classified morphological parameters and small samples (N=15–30), we apply regression analysis and cross-validation. While initial results suggested strong predictive performance, further testing revealed significant instability across subsamples. In particular, model performance degrades substantially for smaller datasets, indicating sensitivity to sample selection. These results suggest a tentative statistical association rather than a robust or universal relationship. The proposed morphology–ADF connection should therefore be interpreted as a preliminary hypothesis requiring validation on larger, independently constructed datasets.