  We calculate the combination $2a_0^{(0)}-5a_0^{(2)}$ (the Olsson sum rule)
and the scattering lengths and effective ranges $a_1$, $a_2^{(I)}$ and $b_1$,
$b_2^{(I)}$ dispersively (with the Froissart--Gribov representation) using, at
low energy, the phase shifts for $\pi\pi$ scattering obtained by Colangelo,
Gasser and Leutwyler (CGL) from the Roy equations and chiral perturbation
theory, plus experiment and Regge behaviour at high energy, or directly, using
the CGL parameters for $a$s and $b$s. We find mismatch, both among the CGL
phases themselves and with the results obtained from the pion form factor. This
reaches the level of several (2 to 5) standard deviations, and is essentially
independent of the details of the intermediate energy region ($0.82\leq E\leq
1.42$ GeV) and, in some cases, of the high energy behaviour assumed. We discuss
possible reasons for this mismatch, in particular in connection with an
alternate set of phase shifts.
