Article
Introduction
Textbooks are compressed representations of what a field considers important to transmit to newcomers. They are written by experts who know a great deal, edited by publishers who want manageable page counts, and reviewed by committees who negotiate scope. The result is a document that reflects the intersection of what experts find interesting, what fits in 600 pages, and what the committee could agree on, which is not necessarily the same as what practitioners need to know.
We focus specifically on the textbook’s most revealing rhetorical gesture: the scope disclaimer. “Beyond the scope of this chapter,” “treatment of this topic requires an entire course,” “the interested reader is directed to” — these phrases function as explicit admissions that the textbook is incomplete, made with the implication that the omitted material is supplementary. We tested this implication empirically.
Catalog Methodology
We identified 47 graduate-level textbooks across six disciplines (statistics, computer science, economics, psychology, biology, and engineering) using citation frequency and adoption rates as selection criteria. We extracted all sentences containing scope-limitation language using a combination of keyword search and manual review, yielding 2,847 instances describing 312 distinct topics.
We then conducted two assessments. First, we surveyed 620 practitioners who had completed graduate programs in the relevant disciplines within the past 5 years, asking how frequently they encountered each topic in their current work. Second, we analyzed 8,400 job postings from the same disciplines, coding for explicit mention of the same topics. Both assessments were conducted by raters blinded to the textbook coverage data.
Results
Of 312 “beyond scope” topics, 244 (78.2%) were reported by at least 25% of practitioners as encountered within 12 months of graduation, and 167 (53.5%) were mentioned in at least 10% of relevant job postings. The most commonly omitted topics, ranked by practitioner encounter frequency, were: (1) debugging code that was written by someone else, (2) communicating statistical results to people who dislike statistics, (3) estimating how long things will take, (4) what to do when the data does not match the model assumptions, and (5) dealing with a reviewer who has clearly not read the paper.
In contrast, we examined the 20 topics receiving the most page coverage in the same 47 textbooks. Eleven of these topics were encountered by fewer than 15% of practitioners in any professional context. The topic with the largest ratio of textbook coverage to practitioner relevance was “proof of the Gauss-Markov theorem,” which appears in a mean of 12.3 pages per textbook and is referenced by 2.4% of practitioners, all of whom report encountering it exclusively while teaching.
Why This Happens
We interviewed 14 textbook authors. The most common explanation for scope limitation was “page count constraints imposed by the publisher” (n=11), followed by “the material requires prerequisites that vary across readers” (n=8), and “honestly I didn’t feel confident enough to write that section” (n=3, all off the record). No author cited “this material is genuinely less important than what we included” as a reason for any omission.
References
- Textbook, T. (2022). “This Topic Is Left As An Exercise For The Reader.” Publisher’s Guidelines for Chapter Length, pp. 44-44.
- Omitted, O. (2023). “A Comprehensive Catalog of Things You Will Need That We Did Not Teach.” Journal of Practical Despair, 1(1), pp. 1-312.
- Gap, C. (2024). “The Gauss-Markov Theorem in Industry: A Survey.” Applied Statistics Quarterly, 18(3), pp. 201-202. (Two pages.)
- Hypothesis, N. (2026). “Treatment of This Topic Is Beyond the Scope of This Paper.” I3E Trashactions on Things Nobody Told The Professor, 1(1), pp. 25-25.