The primordial helium abundance and the number of neutrino families
  Based on observations of HII regions and the new computations of the
recombination coefficients of the He I lines by Porter et al. (2013) we obtain
a primordial helium abundance by mass of $Y_P = 0.2446\pm0.0029$. We consider
thirteen sources of error for the $Y_P$ determination, some of them are mainly
due to systematic effects, while the rest are mainly due to statistical
effects. We compare our results with other determinations of $Y_P$ present in
the literature. Combining our $Y_P$ value with computations of primordial
nucleosynthesis we find a number of neutrino species $N_{eff} = 2.90\pm0.22$,
and a neutron mean life $\tau_{\nu} = 872\pm14(s)$.
