Seeing is believing – the problem of blinding in psychological research

Include “Blog entry written on: “Blinding in randomised clinical trials of psychological interventions: a retrospective study of published trial reports” (bmjebm-2020-111407)

Authors: Sophie Juul, Christian Gluud, Sebastian Simonsen, Frederik Weischer Frandsen, Irving Kirsch, Janus Christian Jakobsen.


Blinding of key persons is rarely reported or implemented in randomised clinical trials of psychological interventions, and only few trialists consider the bias risk this may have caused. Therefore, there is a risk that previous randomised clinical trials of psychological interventions may have overestimated the beneficial effects and underestimated the harmful effects of the experimental interventions being studied.

What is blinding?
Blinding in randomised clinical trials refers to the methodological principle of preventing bias by withholding information about allocation status from individuals or groups. Several studies have demonstrated that lack of blinding is responsible for biased treatment estimates. Therefore, blinding procedures should always be implemented as a methodological safeguard in randomised clinical trials. Ideally, participants, treatment providers, outcome assessors, data managers, data safety and monitoring committee, statisticians, and conclusion makers must be blinded to protect against bias in any trial.

Glasses

What did we do?
We retrospectively studied psychological trial reports published in six high impact factor journals within the field of psychiatry in 2017 and 2018. We assessed the blinding status of key persons involved in the trial. We also assessed if trialists rejected the null hypothesis on the primary outcome measure, and if trialists considered the potential bias risk from lack of blinding when interpreting and reporting the trial results.

What did we find?
Our results showed that blinding of all possible key persons is rarely reported as adequate in randomised clinical trials of psychological interventions. Some key persons are more frequently blinded than others. In our study of trials published in high impact factor journals, 58.7% of the included trials reported adequate blinding of outcome assessors. Participants, treatment providers, data managers, data safety and monitoring committee, statisticians, and conclusion makers were typically either not blinded, or it was unclear whether blinding was performed. It is plausible that the included trials from the selected journals may have underestimated the true bias risk arising from lack of blinding, and that blinding is even less frequently performed or reported if trials from journals with lower journal impact factor had also been included.

Imagine a psychotherapy trial in which the psychotherapist did not know the type of intervention, he or she was delivering. And imagine if the participants neither knew, what psychotherapy type he or she actually received. We discuss if motivated potential therapists who have no or limited knowledge about psychotherapy could be trained and supervised in psychotherapy techniques without knowing the type of psychotherapy, and hence, if participants with no prior experience with psychotherapy may be kept blinded throughout the trial if they are not informed about the specific therapy (the name of the psychotherapy tradition etc.).

Future research
There is a need of randomised clinical trials assessing the effects of psychological interventions with attempts of blinding of all possible key persons. If blinding is not possible to implement, or is not adequately reported, the possible implications when interpreting the trial results should be carefully considered. Future randomised clinical trials of psychological interventions should improve implementation and reporting of blinding status, particularly of trial persons who are easily blinded, i.e. data managers, the data safety and monitoring committee, statisticians, and conclusion makers.


Authors:

Sophie Juul
M.Sc, PhD fellow
1 Stolpegaard Psychotherapy Centre, Mental Health Services in the Capital Region of Denmark, Gentofte, Denmark
2 Department of Psychology, University for Copenhagen, Copenhagen, Denmark
3 Copenhagen Trial Unit, Centre for Clinical Intervention Research, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark

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Christian Gluud
Head of Department
1Copenhagen Trial Unit, Centre for Clinical Intervention Research, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark

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Sebastian Simonsen
M.Sc. PhD.
1 Stolpegaard Psychotherapy Centre, Mental Health Services in the Capital Region of Denmark, Gentofte, Denmark

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Frederik Weischer Frandsen
M.Sc., research assistant
1 Stolpegaard Psychotherapy Centre, Mental Health Services in the Capital Region of Denmark, Gentofte, Denmark

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Irving Kirsch
PhD, Associate director
1 Program in Placebo Studies, Harvard Medical School, Boston, Massachusetts, USA

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Janus Christian Jakobsen
Chief physician, associate professor, PhD
1 Copenhagen Trial Unit, Centre for Clinical Intervention Research, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
2 Faculty of Health Sciences, University of Southern Denmark, Odense, Denmark

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COI: All authors declare that they have no conflicts of interest.


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