  New results based on methods of population synthesis, concerning magnetic
field effects on the evolution of pulsars are reported. The present study
confirms that models with timescales for the magnetic field decay longer than
the pulsar lifetime are in better agreement with data. These new simulations
indicate that the diagram log($P\dot P$) - log($t_s$) alone cannot be used to
test field decay models. The dispersion of the values of the initial period and
magnetic field can explain the observed behaviour of the data points in such a
diagram. The simulations also indicate that the statistical properties of
anomalous X-ray pulsars and soft-gamma repeaters (magnetar candidates) are
compatible with those derived for objects born in the high side tail of the
magnetic field distribution. The predicted birth rate of neutron stars having
field strengths in excess of 10$^{14}$ G is one object born each 750 yr.
