Q: What should I do if I do not have a registration number for my meta-analysis?

In a meta-analysis, the registration number denotes the registration of the protocol used for the meta-analysis. You typically need to register your protocol before starting the meta-analysis, specifically, before starting the data extraction. This is for two reasons.

• When registering your protocol, you can check if there are similar studies being conducted so that you can avoid conducting the same study. (Note that your meta-analysis can still be different as it will address a very specific question and you may choose to look at data and datasets that other researchers may not have. You may also reach different conclusions based on the analysis of the same data.)
• This is also to prevent the possibility of skewing the results based on the data.

Nevertheless, you can still try to register your protocol. If there is still some time for your study to get completed, you may receive the registration number before that and can then submit the number along with the final paper to the journal.

Here are some registry sites:

• PROSPERO: An open registry for all types of systematic reviews
• Cochrane: A registry for systematic reviews of health-care interventions
• Campbell Collaboration: A registry for systematic reviews of social interventions

Additionally, you may also need to provide the completed PRISMA checklist, which is a tool to help you report all the necessary items for a systematic review and meta-analysis. You can find the checklist here: PRISMA Checklist

Related reading:

• Can I competitively register a meta-analysis in PROSPERO?
• A young researcher's guide to a systematic review
• What is the PRISMA checklist?