  In this paper we extend both standard fault tolerance theory and Kitaev's
model for quantum computation, combining them so as to yield quantitative
results that reveal the interplay between the two. Our analysis establishes a
methodology that allows us to quantitatively determine design parameters for a
quantum computer, the values of which ensure that an overall computation of
interest yields a correct *final result* with some prescribed probability of
success, as opposed to merely ensuring that the desired *final quantum state*
is obtained. As a specific example of the practical application of our
approach, we explicitly calculate the number of levels of error correction
concatenation needed to achieve a correct final result for the overall
computation with some prescribed success probability. Since our methodology
allows one to determine parameters required in order to achieve the correct
final result for the overall quantum computation, as opposed to merely ensuring
that the desired final quantum state is produced, our method enables the
determination of complete quantum computational resource requirements
associated to the actual solution of practical problems.
