We revisit the procedure for comparing the ππ spectral function measured in τ decays to that obtained in e + e − annihilation. We re-examine the isospin-breaking corrections using new experimental and theoretical input, and find improved agreement between the τ − → π − π 0 ντ branching fraction measurement and its prediction using the isospin-breaking-corrected e + e − → π + π − spectral function, though not resolving all discrepancies. We recompute the lowest order hadronic contributions to the muon g − 2 using e + e − and τ data with the new corrections, and find a reduced difference between the two evaluations. The new tau-based estimate of the muon magnetic anomaly is found to be 1.9 standard deviations lower than the direct measurement.

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