The defining characteristic of Leitfehler-based methods in automated stammatology is that they weight the variant readings in the various witnesses according to their ability to serve as Leitfehler (or significant variant). They are a subcategory of distance-based methods. Thus the traditional scholarly concept of Leitfehler is taken to be a quantitative one: a variant’s usefulness as Leitfehler may be assigned a number or weight. In classical stemmatology the Leitfehler is the most important tool to arrive at a filiation of witnesses that is believed to be most correct representation. Therefore such automated methods follow the traditional procedure of finding the correct stemma codicum more closely than others that do not take this into account. The effects of weighting variants is a point of debate in the field. Some have explored this open issue and the possibilities for semi-automated weighting (Spencer et al. 2004).
An open challenge in fully automated stemmatology is the estimation of the stemmatological value of a variants computationally. One implementation of such weighting proposed by Roelli (2010 and 2014) is still largely ad hoc, requiring further research and development. This approach tries to evaluate potential candidates for 'good' variants by comparing for every pair of them in what witnesses their absence or presence occurs. If one of the four combinations of absence / presence of any of these two candidates is not represented in any witness, this is taken to be a hint that both variants suffered their change from absence to presence (or vice versa) exactly once in the tradition, which is characteristic for good traditional Leitfehler (Maas 1937). Such a comparison can be made for all combinations of potential Leitfehler while both Leitfehler in pairs with only three combinations get their score increased.
– Maas, Paul. 1937. “Leitfehler und Stemmatische Typen.” Byzantinische Zeitschrift, 37 (2): 289–294.
– Roelli, Philipp, and Dieter Bachmann. 2010. “Towards Generating a Stemma of Complicated Manuscript Traditions: Petrus Alfonsi’s Dialogus.” Revue d’histoire des textes N.S. 5: 307–321.
– Roelli, Philipp. 2014. “Petrus Alfonsi, or :On the Mutual Benefit of Traditional and Computerised Stemmatology.” In Analysis of Ancient and Medieval Texts and Manuscripts: Digital Approaches, edited by Tara Andrews and Caroline Macé, 43–64. Turnhout: Brepols.
– Spencer, Matthew et al. 2004. “The effects of weighting kinds of variants.” In Studies in Stemmatology II, edited by Pieter Th. van Reenen, Aurelius A. den Hollander, and Margot van Mulken, 227–240. Amsterdam: John Benjamins.