  The Sloan Digital Sky Survey (SDSS) was foundational to the study of galaxy
evolution, having revealed the bimodality of galaxies and the relationship
between their structure and star-forming activity. However, ground-based
optical surveys like SDSS are limited in resolution and depth which may lead to
biases or poor quality in the derived morphological properties, potentially
impacting our understanding of how and why galaxies cease their star formation
(quench). We use archival HST imaging of ~2,000 SDSS objects to assess the
reliability of SDSS-derived morphologies, taking advantage of both SDSS
statistical samples and of HST's superior resolution and sensitivity. Single
Sersic fitting and bulge-disk decomposition is performed on HST images for
direct comparison with SDSS results. Of the three catalogs of SDSS-derived
morphologies considered, none are significantly more accurate than the others.
For disk-dominated galaxies (n<2.5), global Sersic indices (n) from Meert et
al. 2015 (M15) are preferred. For bulge-dominated galaxies (n>2.5), Simard et
al. 2011 (S11) and M15 overestimate n by ~20%, and NYU-derived global n are
preferred. Global R_eff from S11 are preferred, but overestimate R_eff for the
largest galaxies by 0.1 dex. SDSS-derived single-component parameters are
generally significantly more robust than SDSS-derived two-component parameters.
The bulge Sersic index (n_bulge) cannot be reliably constrained from SDSS
imaging. The bulge-to-total (B/T) ratio can be reliably inferred from SDSS for
galaxies with SDSS B/T<0.6 provided that n_bulge=4 is enforced. The difference
in global n between HST and SDSS depends strongly on B/T; an empirical
correction based only on it accounts for most of the systematics in global n.
