  We study the relations between spin squeezing and concurrence, and find that
they are qualitatively equivalent for an ensemble of spin-1/2 particles with
exchange symmetry and parity, if we adopt the spin squeezing criterion given by
the recent work (G. Toth et al. Phys. Rev. Lett. 99, 250405 (2007)). This
suggests that the spin squeezing has more intimate relations with pairwise
entanglement. We exemplify the result by considering a superposition of two
Dicke states.
