A model of software reliability that assumes that failures occur according to a Poisson process with a rate decreasing as more faults are discovered. In particular if 0 is the true failure rate per fault and N is the number of faults initially present, then the failure rate for the ith fault (after i 1 faults have already been detected, not introducing new faults in doing so) is 

                                                                    λ = (𝑁 𝑖 + 1 ) ϕ