The Hypothetical and Theoretical Underpinnings of Non-traditional Authorship Attribution Studies: Assumptions, Presumptions, and Verifiable Constructs

Joseph Rudman
Department of English
Carnegie Mellon University
Pittsburgh, PA 15213

I Introduction

Some words, such as "Phrenology" or "Stylometry", insinuate their own assumptions. In fact, nobody has ever proved that minds can be measured by bumps or style by numbers.
Sams [1994] p. 469

In our view the protagonists of stylistic analysis in forensic applications have not only failed to demonstrate such a link [between style and authorship] but have not even attempted to do so.
Totty et al. [1987] p. 18

The hypothesis behind non-traditional authorship attribution studies -- those using the computer, statistics, and stylistics -- is that every author has a verifiably unique style. This paper points out and discusses the fact that this hypothesis has never been empirically tested, let alone proven. The lack of a proven theory after more than thirty years and well over 600 studies is one of the main reasons that non-traditional authorship studies are not accepted --in the main-- by either the literary or the scientific community.

This paper then goes on to discuss some other assumptions behind the main one and finishes by outlining an empirical study to help move the hypothesis to proof. The movement of this hypothesis through theory to proof is needed to give validity to all authorship attribution studies.

II A Short History of the Hypothesis

...try to balance in your own mind the question whether the latter [text] does not deal in longer words than the former [text]. It has always run in my head that a little expenditure of money would settle questions of authorship this way.... Some of these days spurious writings will be detected by this test. Mind, I told you so.
de Morgan [1851] p. 215-216

May there not be "fingerprints" in writing, of which the author, and most of his critics, are quite unconscious, but which could be discovered by some new approach, to the benefit of the search for truth?
Williams [1970] p. 2

This section outlines the history of the hypothesis that every author has a verifiably unique style. Some of the reasons why the hypothesis was never tested are listed with a short discussion (e.g.):

  1. Computers
  2. Machine readable text
  3. Degree of difficulty
  4. The panoply of peripheral disciplines

III What is Behind the Hypothesis: Other Sub-assumptions

Wordprinting is still in its infancy and cannot yet boast an explanatory theory or even an agreed-upon name. Nor do its practitioners agree on an optimal statistical model. This degree of openness...has not prevented the convincing success of a number of important studies, which in turn gives added intuitive plausibility to its basic assumptions.
Reynolds [1995] p. 157

This section lists and discusses some of the sub-assumptions of the main hypothesis:

  1. Style is quantifiable

    That style is quantifiable is now a given -- a fact already established. This quantifiability is what sets the working definition of style for not only this paper, but for most non-traditional authorship attribution studies. A short explanation with examples of empirical studies that prove this point is provided.

  2. Style changes over time

    The problems with this assumption are listed and discussed. Key studies on style change over time are explicated.

  3. Style is different for different genres

    The problems with this assumption are listed and discussed. Key studies on style change over genre are explicated.

  4. Style is as differentiating as (i) Fingerprints, (ii) DNA, or (iii) Iris Scans

    These assumptions differ as to the attainable degree of certainty in any findings. This section goes on to discuss what has been reported in the literature about the degree of certainty and what can and should be expected.

The general problems of non-traditional authorship attribution as reported by Rudman (Rudman, 1998) are discussed only in so far as they have first level bearing on each sub-assumption (e.g.):

  1. Which style markers to use

    Is the number of style markers infinite? Is style an open ended system? (This is a follow-up on a discussion at the Kingstown conference.)

  2. Which statistical tests to use

    Do each of these statistical tests need their own theoretical underpinnings? Michael Farringdon's discussion of the criticism that, "QSUM has no theoretical basis," is explicated.

IV An Empirical Proof

There are two strategies to making progress toward finding the correct underlying theory, (1) the so-called "top-down" approach where one postulates a complete theory of everything... (2) the empirically based "bottom up" approach where one uses experimental data to make smaller, incremental steps.
Rothstein [1998] p. 4

This section discusses the "top-down" and "bottom-up" experimental strategies for moving the hypothesis to a correct theory and thence to studies that can prove or disprove the theory. I have not found a "top-down" approach in the literature -- and, understandably so, if for no other reason than logistics.

One experimental approach to test the hypothesis, a hybrid of the "top-down" and "bottom-up" is given here and discussed:

  1. Within a time period (~ +/- 5 years), language (native), and genre, randomly select (n1)% of all possible writers.

    These constraints eliminate the need to show that a writer's style changes over time, over genre, or language.

  2. Randomly select (n2) passages of (n3) running words from each selected author.

    The question, "How can we be sure that (n2) is truly representative," is discussed.

    The question, "How do we know (n3) is large enough," is discussed.

  3. Subject each author's text to stylistic analysis.

    The statement that, "This should be done using as many style markers as possible," is explicated. A short discussion of the statistics behind the adjudication of each style marker is presented.

  4. Controls:
    1. (n4) other writers from the same pool as (1)
    2. (n5) other selections from the writers selected in (1).

      The determination of each variable "n*" is discussed.

This type of study should be done for every non-traditional authorship attribution study as part of the control. It is important to realize that if this type of control is carried out for every authorship study and if it is consistently shown that every author has a unique style, q.e.d., the hypothesis, is proven!

A survey and critique of some important "bottom-up" studies is presented. The importance of attacking both strategies simultaneously is discussed.

V Conclusion

One salient point made in the conclusion is that assertation is not demonstration. Another point is that the hypothesis has already made important steps towards theory and proof.


De Morgan, Sophia. Memoir of Augustus de Morgan (By his wife Sophia de Morgan, with selections from his letters). London, 1882.

Farringdon, Michael. "The Critics Answered." In Analysing for Authorship. Jill M. Farringdon (with contributions by A. Q. Morton, M. G. Farringdon and M. D. Baker). Cardiff: University of Wales Press, 1996. 239-261.

Reynolds, Noel B. "Statistical Wordprinting." In Thomas Hobbes: Three Discourses. Eds. Noel B. Reynolds and Arlene W. Saxonhouse. Chicago: University of Chicago Press, 1995. 157-162.

Rothstein, Ira Z. "The Search for a Theory of Everything." Interactions (Department of Physics, Carnegie Mellon), 1998, 4.

Rudman, Joseph. "The State of Authorship Attribution Studies: Some Problems and Solutions." Computers and the Humanities, 31(1998), 351-365.

Sams, Eric. "Edmund Ironside and Stylometry." Notes and Queries, Dec. 1994, 469-472.

Totty, R. N. et al., "Forensic Linguistics: The Determination of Authorship from Habits of Style." Journal of the Forensic Science Society, 27(1987), 13-28.

Williams, C. B. Style and Vocabulary: Numerical Studies. London: Charles Griffin & Co., Ltd., 1970.