Consent Forms in Context: How Long is Long?

Mark Hochhauser, Ph.D., Readability Consultant/IRB Member, Golden Valley, MN

Abstract: As the science and regulatory requirements behind clinical trials have evolved over the past few decades, consent forms have become very long. This article compares the word count of some oncology consent forms with other documents, and shows that those consent forms are longer than ethical guidelines and federal regulatory documents. Because too many consent comprehension tests and health literacy measures are not psychometrically sound (and of limited value), efforts to improve comprehension and health literacy continue to be serious problems now and in the future.

As an IRB member for 20 years, I’m concerned about the increasing length of consent forms for clinical trials. Over that time I’ve seen consent forms get so long that I’m not sure any prospective subject can understand them, even if they’re written at the recommended 6th – 8th grade reading level or if those subjects get a reasonable score on a consent comprehension test. There’s simply too much information to read, remember, and analyze. Making an informed decision based on that much information is impossible because no one can process that much information in the relatively short time devoted to reading the consent form and participating in the informed consent conversation.

On the one hand, federal agencies such as the National Cancer Institute have been trying for many years to get researchers to simplify their consent forms by writing more readable consent forms and designing them in more reader-friendly ways. On the other hand, those efforts seem to have little or no effect on how NCI sponsored research consent forms are written: “simplified” consent forms are becoming longer and more complicated!1,2.

In some ways that increasing complexity is not surprising. Decades ago, consent forms were fairly short documents, perhaps only 3 or 4 pages long. But since then, research itself has become more complicated. Early clinical trials compared an experimental drug with a placebo in a fairly straightforward experimental design. But since then, trials have evolved. Current trials include combinations of drugs at different dosages; HIPAA privacy notices have been added, as well as sub-studies involving pharmacogenetics, pharmacokinetics, and plans for future research. New a consent form can include up to five documents, instead of only one. But this kind of research progress is inevitable, and has led to the kind of very long consent forms we see today. As clinical trial research methods and federal regulations keep evolving, consent form materials may become even longer and more complex.

Consent forms in context

Everyone who works with clinical trials and informed consent is aware that consent forms are getting longer. But there’s no perspective on what that means. To make “consent form length” more meaningful, I’ve put them into a broader context by comparing the word count in some oncology consent forms with other research and ethics documents (Table #1).

Table #1: Consent form word counts vs. comparison documents

Words Comparison documents
12,028 ICF for 33 page Phase I clinical trial1
11,720 45 CFR 46 (2009)
  9,500 Longest of 20 oncology consent forms2
  7,471 Average of 20 oncology consent forms2
  7,461 21 CFR 50 (2014)
  5,022 Shortest of 20 oncology consent forms2
  4,934 Belmont Report (1978)
  4,867 NCI Simplification of Informed Consent Documents (2013)
  3,314 NIH: Clinical Research Trials and You:The Basics (2014)
  2,240 Declaration of Helsinki (2013)
  1,599 OCR Model Notice of Privacy Practices (Healthcare Provider)
  1,135 Understanding Informed Consent (CenterWatch)
  1,041 Volunteering for a Trial (CenterWatch)

The longest oncology consent form I’ve reviewed was 12,028 words over 33 single-spaced pages.  As shown in Table #1, that exceeds the word count of all 12 comparison documents.

Even the shortest oncology consent form I reviewed was 5,022 words, making it longer than seven of the comparison documents.

Consent length vs. consent comprehension

One implication this data is that consent comprehension studies done only a few years ago may not generalize to current or future studies. A consent comprehension test developed on consent forms of 1,000 or 2,000 words is not likely to valid for consent forms six times as long. The cognitive skills involved in reading and understanding a fairly short consent form differ greatly the cognitive skills involved in reading and understanding a very long consent form, and those changing cognitive skills will affect consent comprehension.

Can a short consent comprehension test comprised of 10 – 20 questions measure the comprehension of an 8,000 to 12,000 word consent form? At best the test can sample only a small number of topics; a 20 item questionnaire on an 8,000 word consent forms asks the equivalent of one question per 400 words; with a 12,000 words consent form, that 20 item test asks one question for every 600 words.

Unless the comprehension tests become very long (which creates another set of problems), consent comprehension tests aren’t measuring complete comprehension, but only partial comprehension.  A high score (80% or more) on such consent comprehension tests may not mean very much. That’s especially a problem if consent comprehension tests are based on true-false questions (where subjects can get 50% correct by guessing) or multiple-choice questions (where subjects can get 25% correct by guessing). In reality, “fully informed subjects” may not exist.

A recent review of consent comprehension research3 identified 176 possible studies, but only 27 (21%) met the researchers’ criteria.  They found 78% of the studies (21/27) were based on investigator developed comprehension tests; there are not yet any standardized and widely accepted comprehension tests. Plus 74% of the studies (20/27) did not assess prospective subjects’ health literacy and 89% of the studies (24/27) did not report consent form reading grade levels. They found that study subjects had a hard time understanding randomization, placebos, study risks, and many subjects had therapeutic misconceptions about clinical trials.

The researchers noted that clinical trials are expanding worldwide, and will likely involve more vulnerable subject populations, many with problematic literacy skills.  One can only imagine what a 12,028 word English consent form would look like when translated into other languages, and whether international subjects would be able to read and understand that consent form.

Consent length vs. health literacy

Surely health literacy plays a role in the ability of prospective subjects to understand long consent forms. But a recent review4 on that topic looked at 281 studies, of which only six (about 2%) met their eligibility criteria. The researchers noted the methodological problems of using different health literacy measures–and like consent comprehension tests–there were no standardized instruments. Among low literacy subjects, they found little evidence of consent comprehension. While comprehension was improved by having researchers spend more time with prospective subjects, that tentative positive finding was based on only one study.

Thus, health literacy measures suffer from some of the same problems as consent comprehension studies. Based on 301 reviewed articles, a recent review5 of 51 health literacy instruments (about 17%) found that most of their instrument validation procedures were limited by small samples and inadequate statistical power. Those health literacy measures were not reliable or generalizable for different demographic groups.

Equally important, most health literacy instruments lacked information on key psychometric properties of validity and reliability. As with consent comprehension problems described above, these researchers concluded that “…the field still lacks a single rigorously validated health literacy measure that addresses the full range of dimensions which represent this complex construct.” (p. 327).


To better inform prospective subjects, research tries to understand informed consent comprehension. But because of lengthy consent forms and health literacy concerns, researchers have not yet developed psychometrically sound tests to measure either of those critical variables.  It is surprising how many consent comprehension studies and health literacy studies fail to meet the reviewer’s rigorous evaluation criteria; that suggests publication of far too much low-quality research.  To resolve those problems, researchers must develop more scientifically sound methods to define and measure consent comprehension and health literacy, at the same time that consent forms are becoming longer and more complicated.


  1. Hochhauser, M. (2010) Consent Forms are Getting Longer and Longer. SoCRA Source, #66, 75-77/
  2. Hochhauser, M. (2012) The Complexity of Simplified Consent Forms. SoCRA Source, #72, 65-68.
  3. Montalvo, W. & Larson, D. (2014) Participant Comprehension of Research for Which They Volunteer: A Systematic Review. Journal of Nursing Scholarship. Article first published online: 15 AUG 2014. DOI: 10.1111/jnu.12097
  4. Tamariz, L., Palacio, A., Robert, M., et al (2012) Improving the Informed Consent Process for Research Subjects with Low Literacy: A Systematic Review. Journal of General Internal Medicine, 28(1), 121-126. DOI 10.1007/s11606-012-2133-2
  5. Haun, J. N., Valerio, M.A., McCormack, L.A., et al (2014) Health Literacy Measurement: An Inventory and Descriptive Summary of 51 Instruments. Journal of Health Communication: International Perspective, 19 (sup2), 302-333. DOI: 10.1080/10810730.2014.936571

Leave a Reply

Your email address will not be published. Required fields are marked *