---
source: https://iinventedlight.com/library/notes/plain-readability-formulas-limits.md
title: "Readability scores do not prove a text is clear"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "US government work, public domain; original synthesis in our own words"
license_family: usgov
attribution: "Summary by iinventedlight (AI-assisted). Sources: U.S. Securities and Exchange Commission, A Plain English Handbook, US government work, public domain; Centers for Disease Control and Prevention (CDC), CDC Clear Communication Index: User Guide, US government work, public domain."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-09
status: published
checked_on: 2026-11-09
as_of: 2026-11-09
confidence: medium
untested: "Editorial checklist only; not tested with readers. Sources fetched and evidence checked."
category: coverage-gaps
topic_area: "write-edit"
tags: [plain-language, readability, editing, testing]
client: Librarian
sources:
  - id: S1
    title: "A Plain English Handbook"
    publisher: U.S. Securities and Exchange Commission
    url: https://www.sec.gov/pdf/handbook.pdf
    accessed: 2026-11-09
    license: "US government work, public domain"
  - id: S2
    title: "CDC Clear Communication Index: User Guide"
    publisher: Centers for Disease Control and Prevention (CDC)
    url: https://www.cdc.gov/ccindex/pdf/clear-communication-user-guide.pdf
    accessed: 2026-11-09
    license: "US government work, public domain"
---
# Readability scores do not prove a text is clear

**Answer:** Readability formulas count syllables, words, and sentences; none takes into account the content of the document or whether you have conveyed the information clearly.

## Evidence from two federal guides

- SEC handbook: no formula can tell you if you have conveyed the information clearly; by some formulas, Einstein's theory of relativity reads at a 5th grade level.
- Computerized style checkers identify the passive voice and may suggest ways to make writing more readable; take their suggestions as just that.
- CDC Clear Communication Index: readability formulas are inadequate to assess communication effectiveness; they don't consider audience, purpose, or most characteristics that contribute to clarity and comprehension.
- CDC: short words and sentences help some aspects of cognitive processing but are not sufficient to ensure clear communication.

## What to do instead

The final test of whether writing meets its goal of communicating information comes when humans read it.

## See also

- [plain-language-test-with-readers](https://iinventedlight.com/library/notes/plain-language-test-with-readers/)
- [plain-score-with-clear-communication-index](https://iinventedlight.com/library/notes/plain-score-with-clear-communication-index/)

## Claims

- id: C1
  claim: No readability formula takes content into account.
  source: S1
  evidence: "No formula takes into account the content of the document being evaluated."

- id: C2
  claim: Final test is human readers.
  source: S1
  evidence: "test of whether any piece of writing meets its goal of communicating"

- id: C3
  claim: CDC calls readability formulas inadequate.
  source: S2
  evidence: "Readability formulas are inadequate to assess communication effectiveness."

- id: C4
  claim: Short words and sentences are not sufficient.
  source: S2
  evidence: "they are not sufficient for ensuring that communication is clear and effective"

## Sources

- [S1] A Plain English Handbook. U.S. Securities and Exchange Commission. https://www.sec.gov/pdf/handbook.pdf . License: US government work, public domain. Accessed 2026-11-09.

- [S2] CDC Clear Communication Index: User Guide. Centers for Disease Control and Prevention (CDC). https://www.cdc.gov/ccindex/pdf/clear-communication-user-guide.pdf . License: US government work, public domain. Accessed 2026-11-09.


License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted). Sources: US federal government works (GSA, GPO, SEC, CDC), public domain in the United States; third-party quotations inside those works were not used. Text was condensed and changed from the originals.

---

Agents: [/agents.md](/agents.md) | [/.well-known/agent-library.json](/.well-known/agent-library.json).