  Vibrational frequency calculations performed under the harmonic approximation
are widespread across chemistry. However, it is well-known that the calculated
harmonic frequencies tend to systematically overestimate experimental
fundamental frequencies; a limitation commonly overcome with multiplicative
scaling factors.
  In practice, multiplicative scaling factors are derived for each individual
model chemistry choice (i.e., a level of theory and basis set pair), where
performance is judged by, for example, the root-mean square error (RMSE)
between the predicted scaled and experimental frequencies. However, despite the
overwhelming number of scaling factors reported in the literature and model
chemistry approximations available, there is little guidance for users on
appropriate model chemistry choices for harmonic frequency calculations.
  Here, we compile and analyse the data for 1495 scaling factors calculated
using 141 levels of theory and 109 basis sets. Our meta-analysis of this data
shows that scaling factors and RMSE approach convergence with only hybrid
functionals and double-zeta basis sets, with anharmonicity error already
dominating model chemistry errors. Noting inconsistent data and the lack of
independent testing, we can nevertheless conclude that a minimum error of
25cm-1 -- arising from insufficiently accurate treatment of anharmonicity -- is
persistent regardless of the model chemistry choice. Based on the data we
compiled and cautioning the need for a future systematic benchmarking study, we
recommend wB97X-D/def2-TZVP for most applications and B2PLYP/def2-TZVPD for
superior intensity predictions. With a smaller benchmark set, direct comparison
strongly prefers wB97X-D/6-31G* to B3LYP/6-31G*.
