Background: Although the amount of detail in informed consent documents has increased over time and the documents have therefore become very long, there is little research on whether longer informed consent documents actually result in (1) better informed research subjects or (2) higher consent rates. We therefore conducted an add-on randomized controlled trial to the Takashima Study, a prospective Japanese population-based genetic cohort study, to test the hypothesis that a shorter informed consent form would satisfy both of the above goals.
Methods: Standard (10 459 words, 11 pages) and short (3602 words, 5 pages) consent forms in Japanese were developed and distributed using cluster-randomization to 293 potential cohort subjects living in 9 medico-social units and 288 subjects in 8 medico-social units, respectively.
Results: Few differences were found between the 2 groups with regard to outcome measures, including participants' self-perceived understanding, recall of information, concerns, voluntariness, trust, satisfaction, sense of duty, and consent rates.
Conclusions: A short informed consent form was no less valid than a standard form with regard to fulfilling ethical requirements and securing the scientific validity of research.