Textual Stability of NT Writings
One of the most interesting studies I’ve read recently is by K. Martin Heide (Munich University), entitled “Assessing the Stability of the Transmitted Texts of the New Testament and the Shepherd of Hermas,” which appears in a forthcoming book, The Reliability of the New Testament: Bart Ehrman and Daniel Wallace in Dialogue, ed. Robert B. Stewart (Minneapolis: Fortress Press, 2011), pp. 111-145.
Essentially, Heide does a quantitative analysis of the extent of textual variation across early centuries in NT manuscripts, and then the same with manuscripts of the extra-canonical text, The Shepherd of Hermas. (Because the very earliest manuscripts of all these texts are fragmentary, Heide focuses on passages extant in the earliest witnesses, using them as test-passages.)
His calculations for the NT manuscripts included show an average textual stability of 92.6% (of the words in the test passages), the spread of results for individual manuscripts ranging from 87.1% to 99.7%.
To achieve some perspective, Heide then conducts the same sort of analysis of extant manuscripts of Shepherd of Hermas (the single most frequently copied extra-canonical text, and more frequently copied than most canonical texts in the first several centuries). The average stability is ca. 86%. Heide notes that this doesn’t “even reach the worst value of the New Testament text, as reprsented by P45 [the Chester Beatty Gospels codex].”
Heide’s judgement is that “the reproduction of the New Testament writings was subject to greater scrutiny” (136), and in the case of Shepherd and also other extra-canonical texts (e.g., Epistle of Barnabas, Protevangelium of James), “Theological interests and piety destabilised the text of these manuscripts far beyond the stability of the text of the canonical gospels” (138).