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. 2023 Apr 18;13(4):e069553. doi: 10.1136/bmjopen-2022-069553

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© Author(s) (or their employer(s)) 2023. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

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Percentage of retrospectively registered (RR) trials over time (per study start year). Generalised additive model smoother laid over (blue) with 95% CI. Bubble sizes indicate the number of trials per year included in the dataset.