  As a guideline for future experiments to extract the four (leading) spin
polarizabilities of the nucleon, we have constructed the forward amplitude for
polarized Compton scattering by dispersion integrals. These integrals have been
saturated by recently measured helicity-dependent photoabsorption cross
sections as well as predictions for pion photoproduction multipoles from
several phenomenological descriptions and chiral perturbation theory. The
comparison of these results corroborates the strategy to extract the spin
polarizabilities by fitting them to polarized Compton data and fixing all
higher order spin effects by dispersion relations based on pion photoproduction
multipoles.
