  We investigate the structure of the experimentally significant electroweak
bosonic loop corrections to the leptonic weak mixing angle, the leptonic
Z-boson decay width, and the W-boson mass. It is shown that the bosonic
corrections that have a sizable effect at the present level of experimental
accuracy are directly related to the use of the Fermi constant G_F as input
parameter for analyzing the LEP observables. Indeed, if the (theoretical value
of the) leptonic width of the W boson is used as input parameter instead of the
low-energy parameter G_F determined from muon decay, fermion-loop corrections
are sufficient for compatibility between theory and experiment.
