neutron source in an ACU could generate a gamma-ray via inelastic scattering in the stainless steel vessel before subsequently being captured on Fe/Cr/Mn/Ni. An IBD is mimicked if both gamma-rays from the scattering and capture processes enter the scintillator. This correlated background is estimated using MC. The normalization is constrained by the measured rate of single delayed-like candidates from this source.

Oscillation analyses {#oscillation}
====================

Early results of Daya Bay were based on rate analysis when the statistics were low. The rate deficit at the far site was $\sim6$% compared to the prediction based on a weighted combination of two near site measurements. The value of $\sin^22\theta_{13}$ is determined with a $\chi^2$ constructed with pull terms accounting for the correlation of the systematic errors, $$\begin{aligned}
  \label{eqn:chi2}
 \chi^2 &=&
 \sum_{d=1}^{6}
 \frac{\left[M_d-T_d\left(1+  \varepsilon
 + \sum_r\omega_r^d\alpha_r
 + \varepsilon_d\right) +\eta_d\right]^2}
 {M_d+B_d}  \nonumber \\
 &+&
 \sum_r\frac{\alpha_r^2}{\sigma_r^2}
 + \sum_{d=1}^{6} \left(
 \frac{\varepsilon_d^2}{\sigma_d^2}
 + \frac{\eta_d^2}{\sigma_{B}^2}
 \right)
 \,,\end{aligned}$$ where $M_d$ are the measured number of IBD events of the $d$-th AD with its backgrounds subtracted, $B_d$ is the corresponding background, $T_d$ is the prediction from antineutrino flux, including MC corrections for energy responses and neutrino oscillations, $\omega_r^d$ is the fraction of IBD contribution of the $r$-th reactor to the 