We undertake a covariance error analysis of the pion-nucleon-nucleon coupling constants from the Granada-2013 $np$ and $pp$ database, comprising a total of 6720 scattering data below laboratory energy of 350 MeV. Assuming a unique pion-nucleon coupling constant in the one-pion exchange potential above a boundary radius rc=30.16em0exfm we obtain f²=0.0763(1). The effects of charge symmetry breaking on the ³P₀, ³P₁, and ³P₂ partial waves are analyzed and we find fₚ²=0.0761(4), f₀²=0.0790(9), and fc²=0.0772(6) with a strong anticorrelation between fc² and f₀². We successfully test normality for the residuals of the fit. Potential tails in terms of different boundary radii as well as chiral two-pion-exchange contributions as sources of systematic uncertainty are also investigated.
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Pérez et al. (2017) studied this question.