  We propose a new correlator in one-dimensional quantum spin chains, the
$s-$Emptiness Formation Probability ($s-$EFP). This is a natural generalization
of the Emptiness Formation Probability (EFP), which is the probability that the
first $n$ spins of the chain are all aligned downwards. In the $s-$EFP we let
the spins in question be separated by $s$ sites. The usual EFP corresponds to
the special case when $s=1$, and taking $s>1$ allows us to quantify non-local
correlations. We express the $s-$EFP for the anisotropic XY model in a
transverse magnetic field, a system with both critical and non-critical
regimes, in terms of a Toeplitz determinant. For the isotropic XY model we find
that the magnetic field induces an interesting length scale.
