oscillation parameters is to construct a $\chi^2$ expression using a covariance matrix $$\label{eq:chi22}
  \chi^{2} = \sum_{i,j}(N_j^{\mathrm{f}} - w_j \cdot N_j^{\mathrm{n}}) (V^{-1})_{ij} (N_i^{\mathrm{f}} - w_i \cdot N_i^{\mathrm{n}}),$$ where $N_i$ is the observed number of events after background subtraction in the $i$-th bin of reconstructed positron energy. The superscript $f~(n)$ denotes a far (near) detector. The symbol $V$ represents a covariance matrix that includes known systematic and statistical uncertainties. The quantity $w_i$ is a weight that accounts for the differences between the near- and far-site measurements. In this method, the flux and spectrum of the antineutrinos at the reactor play a negligible role [@DB_2015]. The results from the fit shown in the $\sin^22\theta_{13}$-$\Delta m^2_{ee}$ plane are depicted in Fig. \[fig:contours\].

![Error contours corresponding to the $68.3\%$, $95.5\%$ and $99.7\%$ confidence levels in the $|\Delta m^{2}_{\mathrm{ee}}|$-$\sin^{2}2\theta_{13}$ plane. The contours were obtained with a least-squares fit given in Eq. \[eq:chi22\] using the measured $\overline{\nu}_e$ rates and energy spectra at the near and far sites. The adjoining panels show the dependence of $\Delta\chi^{2}$ on $\sin^{2}2\theta_{13}$ (top) and $|\Delta m^2_{\mathrm{ee}}|$ (right). Figure adapted from [@DB_2015]. \[fig:contours\]](farNearAllowedOscillation_621days_wAccel_v5.pdf){width="60.00000%"}

Daya Bay has also accumulated an IBD sample with neutron capture on hydrogen (nH) which has comparable statistics to that 