  We investigate the effects of dust extinction on integrated absorption-line
indices that are widely used to derive constraints on the ages and
metallicities of composite stellar systems. Typically, absorption-line studies
have been performed on globular clusters or elliptical galaxies, which are
mostly dust-free systems. However, many recent studies of integrated stellar
populations have focused on spiral galaxies which may contain significant
amounts of dust. It is almost universally assumed that the effects of dust
extinction on absorption-line measurements are entirely negligible given the
narrow baseline of the spectral features, but no rigorous study has yet been
performed to verify this conjecture. In this analysis, we explore the
sensitivity of the standard set of Lick absorption-line indices, the
higher-order Balmer line indices, the 4000 A break, the near-IR calcium triplet
indices, and the Rose indices to dust absorption according to population
synthesis models that incorporate a multi-component model for the line and
continuum attenuation due to dust. The latter takes into account the finite
lifetime of stellar birth clouds. While dust does not greatly affect the
line-index measurements for single stellar populations, its effect can be
significant for the 4000 A break or when there is a significant amount of
current star formation.
