Difference between individual stellar parallaxes and the group parallax as a function of G′ for the stars in Villafranca O-001 to Villafranca O-013 plus Villafranca O-015 and Villafranca O-016. The data have been binned to see the effect as a function of magnitude. The horizontal error bars show the extent of G′ magnitudes binned and the vertical error bars show the weighted standard deviation of the mean using as inputs the values with the external uncertainties.