One difficulty in interpreting these studies by Howard, Patterson and their colleagues is that in each case a claim is made concerning average effects of treatment/facilitation for patients with naming deficits even though the patients may have had heterogeneous underlying causes of their naming problems. Similar criticisms apply to claims from single-subject studies of treatment for some ´class´ of lexical disorders. For example, de Partz (1986) described treatment of ´deep dyslexia´ that involved re-teaching sound-spelling correspondences. Their patient (like P.M. noted earlier) improved in oral reading of words (and non-words) using this strategy. But improved oral reading would be a useful gain only for those patients in whom the problem that underlies the behaviours classified as ´deep dyslexia´ stems from damage to the phonological output lexicon.