We compute quasilinear diffusion rates due to pitch-angle scattering by various mechanisms in the Earth’s electron radiation belts. The calculated theoretical lifetimes are compared with observed decay rates and we find excellent qualitative agreement between the two. The overall structure of the observed lifetime profiles as a function of energy and is largely due to plasmaspheric hiss and Coulomb scattering. The results also reveal a local minimum in lifetimes in the inner zone at lower energy (~50 keV), attributed to enhanced scattering via ground-based VLF transmitters, and a reduction in lifetimes at higher and energy (>1 MeV), attributed to enhanced EMIC wave scattering. In addition, we find significant quantitative disagreement at <3.5, where the theoretical lifetimes are typically a factor of ~10 larger than the observed, pointing to an additional loss process that is missing from current models. We discuss potential factors that could contribute to this disagreement.