The use of quantitative approaches to style and authorship studies predated computing. In a letter written in 1851 mathematician and logician Augustus De Morgan proposed a quantitative study of vocabulary as a means of investigating the authorship of the Pauline Epistles.
Lord, R. D. "Studies in the History of Probability and Statistics: viii. de Morgan and the Statistical Study of Literary Style," Biometrika 45 (1851) 282.
A Companion to Digital Humanities, ed. Susan Schreibman, Ray Siemens, John Unsworth. Oxford: Blackwell, 2004.