Q: Can I correct a registered clinical trial protocol after completion of a study?
I have registered a calculation method of sample size in a clinical trial registry in advance, but after completion of a study, I found that the calculation method was wrong. The actual sample size should be smaller. Can I submit a manuscript to an international journal with corrected sample size? If I can submit like that, should I mention the correction of sample size on the cover letter or anywhere?
Clinical trials specify endpoints that will be assessed in advance to avoid any bias in the study. However, sometimes changes may be required after the start of the trial. In such cases, it is best to make a formal amendment to the trial registration.
In your case, if you feel that the change in sample size is justified, I think you should first submit the amended protocol to the trial registry. While waiting for the protocol to get updated, you can submit the manuscript to your target journal with clarifications regarding the amendment mentioned clearly in the cover letter. Since the journal review time is usually fairly long, the amended protocol will probably be updated in the registry by the time your article is published. That way, you can avoid contradictions/controversies about the mismatch with the protocol after your article has been published.
You might find the following articles interesting:
- A young researcher's guide to a clinical trial
- SLIDE DECK: An introduction to clinical trials (Part 1: The basics)
- SLIDE DECK: An introduction to clinical trials (Part 2: Things to remember)
- 3 Signs of poorly designed clinical trial protocol [Includes research protocol checklist]
- What every medical researcher should know about registering clinical trials
- Ethical requirements for clinical trials