The influence of experimental uncertainties of calorimetric parameters from heat capacity spectroscopy on the temperature-dependent glass transition cooperativity N-alpha from the fluctuation approach is studied. Glass transition parameters from 3 omega method and temperature modulated DSC are compared. The influence of the stationary temperature field on the output of the 3 omega method is studied. Special advantages and disadvantages of 3 omega method and temperature modulated DSC for the determination of glass transition cooperativity are discussed. It is confirmed that the temperature-dependent cooperativity indicates, independent from experimental uncertainties, a cooperativity onset in the crossover region. The extrapolated onset temperature T,,, from calorimetry is shown to be comparable with other, independently obtained crossover temperatures for polystyrene and styrene butadiene rubber (SBR 1500).