  The $^{12}$C+$^{12}$C fusion reaction plays a crucial role in stellar
evolution and explosions. Its open reaction channels mainly include $\alpha$,
$p$, $n$, and ${}^{8}$Be. Despite more than a half century of efforts, large
discrepancies remain among the experimental data measured using various
techniques. In this work, we analyze the existing data using the statistical
model. Our calculation shows: 1) the relative systematic uncertainties of the
predicted branching ratios get smaller as the predicted ratios increase; 2) the
total modified astrophysical S-factors (S$^*$ factors) of the $p$ and $\alpha$
channels can each be obtained by summing the S$^*$ factors of their
corresponding ground-state transitions and the characteristic $\gamma$ rays
while taking into account the contributions of the missing channels to the
latter. After applying corrections based on branching ratios predicted by the
statistical model, an agreement is achieved among the different data sets at
${E}_{cm}>$4 MeV, while some discrepancies remain at lower energies suggesting
the need for better measurements in the near future. We find that the recent
S$^*$ factor obtained from an indirect measurement is inconsistent with the
direct measurement at energies below 2.6 MeV. We recommend upper and lower
limits for the ${}^{12}$C+${}^{12}$C S$^*$ factor based on the existing models.
A new $^{12}$C+$^{12}$C reaction rate is also recommended.
