  We present a statistical analysis of the interstellar medium (ISM)
polarization from the largest compilation available of starlight data, which
comprises ~ 5500 stars. The measured correlation between the mean polarization
degree and extinction indicates that ISM dust grains are not fully aligned with
the uniform component of the large-scale Galactic magnetic field. Moreover, we
estimate the ratio of the uniform to the random plane-of-the-sky components of
the magnetic field to be B_u/B_r = 0.8. From the analysis of starlight
polarization degree and position angle we find that the magnetic field broadly
follows Galactic structures on large-scales. On the other hand, the angular
power spectrum C_l of the polarization degree for Galactic plane data is found
to be consistent with a power-law, C_l ~ l^{-1.5} (where l = 180 deg/\theta is
the multipole order), for angular scales \theta > 10 arcmin. We argue that this
data set can be used to estimate diffuse polarized emission at microwave
frequencies.
