Are you allowed to present data on those who declined to participate in your study?

The following is an excerpt from a study on whiplash-traumas where the authors clearly publish some basic statistics on people who declined to participate [1].

Emergency departments identified 6952 eligible participants, of which 3851 (55%) agreed to provide follow-up data (figure). People who participated were older (mean age 37 years vs 32 years) and more likely to be female (2133 [55%] of 3851 vs 1435 [42%] 3430) than the patients who did not participate, but not different in whiplash associated disorder grade.

[1] Lamb SE, Gates S, Williams M a., Williamson EM, Mt-Isa S, Withers EJ, et al. Emergency department treatments and physiotherapy for acute whiplash: A pragmatic, two-step, randomised controlled trial. Lancet [Internet]. Elsevier Ltd; 2013;381(9866):546–56. Available from: http://dx.doi.org/10.1016/S0140-6736(12)61304-X

  • What is your worry here, exactly?
    – vonbrand
    Commented Sep 8, 2015 at 9:48
  • 2
    @vonbrand That it would be unethical to include data on someone who did not want to participate. Commented Sep 8, 2015 at 11:26
  • If the only thing reported is the number of non-participants, and there is are enough population to making identification of participants/non-participants next to impossible, I don't see a problem.
    – vonbrand
    Commented Sep 8, 2015 at 19:26
  • @vonbrand: I agree, though in my example the authors also compared the diagnoses of participants with those of non-participants. Commented Sep 13, 2015 at 17:52
  • Note that the above study is looking at people who declined to provide follow-up data. That says nothing about the basic demographic and diagnostic data the study already had access to.
    – Fomite
    Commented Jan 11, 2016 at 19:40

2 Answers 2


This is standard practice. And it is necessary in order to detect selection bias.

The CONSORT initiative (Consolidated Standards of Reporting Trials) provides a flow chart that includes entries for "declined to participate" and dropouts in various follow-ups.

The American Psychological Association, in its Ethical Principles for Psychologists and Code of Conduct, section 8.05 "Dispensing with Informed Consent for Research", writes:

Psychologists may dispense with informed consent only (1) where research would not reasonably be assumed to create distress or harm and involves (a) the study of normal educational practices, curricula, or classroom management methods conducted in educational settings; (b) only anonymous questionnaires, naturalistic observations or archival research for which disclosure of responses would not place participants at risk of criminal or civil liability or damage their financial standing, employability or reputation, and confidentiality is protected; or (c) the study of factors related to job or organization effectiveness conducted in organizational settings for which there is no risk to participants' employability, and confidentiality is protected or (2) where otherwise permitted by law or federal or institutional regulations.

The kind of summary statistics you cite falls squarely under point 1b.

Of course, you do need to exercise some caution, in particular to ensure that confidentiality is maintained. Listing the names of non-participants, for instance, would certainly cross the line. As would giving out "too much" information from which one could reasonably deduce the identities of participants or non-participants (if you work with a small, easily identified population, say).


It seems to me that this is clearly relevant to the study. As long as no personally identifiable data (and just the numbers cited clearly don't qualify as that) I don't see a problem.

In the end, "declined to participate" is an indicator of some self-selection, which could introduce some bias.


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