Results in 2013 from [[Planck (spacecraft)|Planck]] mission, in combination with data from WMAP polarization, small-scale CMB experiments, and [[Baryon acoustic oscillations|BAO]] measurements yield an instantaneous reionization redshift of z = 11.3 ± 1.1 [REF].
The parameter usually quoted here is τ, the "optical depth to recombination," or alternatively, z<sub>re</sub>, the redshift of reionization, assuming it was an instantaneous event.