  Dispersive sum rules constitute long-standing tools for extracting hadron
features from QCD. We estimate the systematic uncertainties induced by assuming
quark-hadron duality and improve the accuracy of the resulting predictions by
elevating the effective thresholds involved in this approximation from
constants to functions of momenta and a parameter entering upon Borel
transformation. A rigorous scrutiny of the applicability of our proposed
sum-rule modifications to QCD gives us great confidence that our sum-rule
alterations will prove to be fruitful for hadron phenomenology.
