Left panel: distribution of correlation coefficients of the oxygen abundance along the radial distance, for the 193 galaxies described in the text. Central panel: distribution of zero points for the corresponding linear regression galaxy by galaxy. Right panel: distribution of slopes of the same regressions. The orange solid line represents, for each of the last two histograms, the expected histogram in case of a Gaussian distribution of the data, assuming the mean and standard-deviation of the distribution of each analyzed parameter and sampled with the same bins.