We are planning to do a fully remote clinical trial to test an online intervention for depression. We will be using a self-rated PHQ-9 at base-line, post intervention, and 90 days follow-up to test the efficacy of the intervention.

The participants wouldn't know if they are assigned to the experimental or the control group (so it is definitely single-blind). Since there is no investigator who will be assessing the depression severity, there is no source of any human bias there (since double-blind trials are designed to eliminate investigator bias).

I was wondering if this can be called a double-blind study. I have seen other fully remote trials with a similar design but they haven't mentioned the term double-blind anywhere. Considering the fact that it is the gold standard, I am surprised that investigators did not mention it in their paper. That is the source of my confusion.

Any thoughts are welcome. Thanks in advance.


Double blind basically consists when the patient does not know to which condition it belongs (control, treatment A, treatment B) and the professional does not know to which group he/she is administering the treatment (control, treatment A, treatment B).

The double-blind designation is not based on the fact that the initial level of depression is not assessed. (I guess you know it and it has been erroneously specified in the question).

In online studies this denomination is not usually used although of course it is not incompatible. (The issue is that this denomination is not usually used because the trial is not common either).

In short I do not see problem with the double blind designation.

On the other hand, it would be necessary to pay close attention to the clinical level and the characteristics of the intervention (you do not specify, is the intervention also remote?).

In any case sounds very interesting.

  • $\begingroup$ What I meant by this line "Since there is no investigator ... source of any bias there." is that there is no source of investigator bias which is generally eliminated by masking an investigator. I guess that didn't come off correctly in my question. I'll re-frame it. Yes, the intervention is fully stand-alone and online. I too think that the double-blind designation is fine, but I haven't seen it mentioned in other papers. Considering the fact that it is the gold standard, I am surprised that investigators will not mention it in their paper. $\endgroup$ – Arka Ghosh Jul 18 '17 at 14:58
  • $\begingroup$ Okay, I do not see problem either. To some extent the highest quality assay is currently considered to be the randomized controlled trial. $\endgroup$ – hexadecimal Jul 18 '17 at 15:13
  • $\begingroup$ Yeah. More specifically, it is multi-centric double-blinded randomized controlled trial. $\endgroup$ – Arka Ghosh Jul 18 '17 at 15:15

If the investigator knows what group the subject is in and then has any interaction with the subject, it is not double blind since the investigator can, potentially unintentionally, influence the subject. The fact that the measures are objective is irrelevant.

  • $\begingroup$ Yes, that is true. In our trial there will be no in person interaction with participants of either the experimental or the control group. However, there is a forum in the experimental group where everyone, participants and investigators, will be able to post questions and answer questions. But, that is an extra feature of the experimental group which we think will help participants with their problems. We'll have to think carefully about this interaction. $\endgroup$ – Arka Ghosh Jul 18 '17 at 16:57

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