Left panel: this panel demonstrates how the marginalized one-dimensional posterior distribution of ∑ m _ν changes when a single external data set is added to the CMB data set. The CMB constraint is shown by the black solid line. The data sets added are the BAO data (blue dot-dashed line), H ₀ measurement (blue dashed line), LRG sample (black dotted line), and SPT cluster data (orange solid line). Right panel: this panel demonstrates how the marginalized one-dimensional posterior distribution of ∑ m _ν changes when a single external data set is removed from the combination of CMB+BAO+ H ₀ + . The data sets dropped are the SPT bandpowers (orange solid line), (blue dashed line), BAO data (blue dot-dashed line), and H ₀ measurement (black dotted line). The marginalized posterior for the combined CMB+BAO+ H ₀ + data set is shown by the black solid line.