We compare and contrast the error probability and fidelity as measures of t
he quality of the receiver's measurement strategy for a quantum communicati
ons system. The error probability is a measure of the ability to retrieve c
lassical information and the fidelity measures the retrieval of quantum inf
ormation. We present the optimal measurement strategies for maximizing the
fidelity given a source that encodes information on the symmetric qubit-sta
tes.