External validity of a randomised clinical trial of temporomandibular disorders: analysis of the patients who refused to participate in research

Br J Oral Maxillofac Surg. 2003 Apr;41(2):129-31. doi: 10.1016/s0266-4356(03)00037-8.


Purpose: To assess the external validity of a randomised clinical trial (RCT) of a painful condition.

Method: Consecutive patients with painful temporomandibular disorders (TMDs) were invited to participate in a clinical trial. Patients who refused to participate were compared to those who agreed to participate in this study with respect to degree of symptoms at time of presentation.

Results: The patients who refused to participate had more pain, and their condition interfered more with their daily life than those who accepted the invitation to participate.

Conclusion: Selection bias in RCTs of painful conditions can skew the results, and external validity should be analysed before the results are generalised.

Publication types

  • Comparative Study
  • Validation Study

MeSH terms

  • Activities of Daily Living
  • Adolescent
  • Adult
  • Aged
  • Anti-Inflammatory Agents, Non-Steroidal / therapeutic use
  • Exercise Therapy
  • Follow-Up Studies
  • Humans
  • Middle Aged
  • Pain Measurement
  • Randomized Controlled Trials as Topic / statistics & numerical data*
  • Range of Motion, Articular / physiology
  • Selection Bias
  • Statistics, Nonparametric
  • Temporomandibular Joint Disorders / physiopathology
  • Temporomandibular Joint Disorders / therapy*
  • Treatment Refusal / statistics & numerical data*


  • Anti-Inflammatory Agents, Non-Steroidal