  We have investigated the model dependence of meson resonance properties
extracted from the Dalitz-plot analysis of the three-pions photoproduction
reactions on the nucleon. Within a unitary model developed in Phys. Rev. D 84,
114019 (2011), we generate Dalitz-plot distributions as data to perform an
isobar model fit that is similar to most of the previous analyses of three-pion
production reactions. It is found that the resonance positions from the two
models agree well when both fit the data accurately, except for the resonance
poles near branch points. The residues of the resonant amplitudes extracted
from the two models and by the usual Breit-Wigner procedure agree well only for
the isolated resonances with narrow widths. For overlapping resonances, most of
the extracted residues could be drastically different. Our results suggest that
even with high precision data, the resonance extraction should be based on
models within which the amplitude parametrization is constrained by
three-particle unitarity condition.
