A novel approach, the identity method, was used for particle identification
and the study of fluctuations of particle yield ratios in Pb+Pb collisions at
the CERN Super Proton Synchrotron (SPS). This procedure allows to unfold the
moments of the unknown multiplicity distributions of protons (p), kaons (K),
pions (π) and electrons (e). Using these moments the excitation function of
the fluctuation measure νdyn[A,B] was measured, with A and
B denoting different particle types. The obtained energy dependence of
νdyn agrees with previously published NA49 results on the related
measure σdyn. Moreover, νdyn was found to depend
on the phase space coverage for [K,p] and [K,π] pairs. This feature most
likely explains the reported differences between measurements of NA49 and those
of STAR in central Au+Au collisions
