Consistency checks of pion-pion scattering data and chiral dispersive   calculations
  We have evaluated forward dispersion relations for scattering amplitudes that follow from direct fits to several sets of pion-pion scattering experiments, together with the precise K decay results, and high to energy data. We find that some of the most commonly used experimental sets, as well as some recent theoretical analyses based on Roy equations, do not satisfy these constraints by several standard deviations. Finally, we provide a consistent pion-pion amplitude by improving a global fit to data with these dispersion relations. 
J. R. Pelaez and F.J. Yndurain