  Quantum error mitigation (QEM) is a promising technique of protecting hybrid
quantum-classical computation from decoherence, but it suffers from sampling
overhead which erodes the computational speed. In this treatise, we provide a
comprehensive analysis of the sampling overhead imposed by QEM. In particular,
we show that Pauli errors incur the lowest sampling overhead among a large
class of realistic quantum channels having the same average fidelity.
Furthermore, we show that depolarizing errors incur the lowest sampling
overhead among all kinds of Pauli errors. Additionally, we conceive a scheme
amalgamating QEM with quantum channel coding, and analyse its sampling overhead
reduction compared to pure QEM. Especially, we observe that there exist a
critical number of gates contained in quantum circuits, beyond which their
amalgamation is preferable to pure QEM.
