 On the other hand, if the likelihood principle is to be followed consistently, then the likelihood ratio of the original outcome should be used and not formula_14, making the basis of such an interpretation questionable.Birnbaum later described this as having "at most heuristic, but not substantial, value for evidential interpretation".A more direct approach leading to a similar conclusion can be found in Birnbaum's formulation of the "Confidence principle", which, unlike the more common version, refers to error probabilities of both kinds.