Percent of trials with enrollment year preceding registration year (1999-2024)

Published: December 2024, data up to June 2024

The analysis includes data on all retrospective trial registrations reported in the WHO International Clinical Trials Registry Platform (ICTRP) for the period 1999 to mid-2024. Retrospective registration is a registration of a trial after enrollment of the first participant. In general WHO discourages retrospective registration for a number of reasons, although retrospective in a short timeframe (no more than a few weeks from first enrollment) is preferable to no registration at all. See more on scope of ICTRP below.

See also: 

What you see | Scope and limitations | Data sources | Previous versions

What you see

Chart A shows the trial registration for the period 1999 to June 2024 by year, colour-coded by WHO region. Chart B shows the percent of trials with the enrollment year preceding the registration year by WHO region.

Points to note:

• Globally, there has been a steady increase in the number of trial registrations in ICTRP during the 1999–2021 period, and a decrease since then. Trials are predominantly registered in three WHO regions: Americas, Europe and the Western Pacific. The WHO region in which the fewest trials are registered in ICTRP, is Africa (select Africa in the Region key, chart A).
• Although in 2023, the majority of trials are registered within one year of first enrollment especially in South-East Asia region where only 4% of trials are registered after enrolment has started. In other regions however 15-25% of trials remain unregistered after one year (hover over the point for the year 2022 on the line representing the region in chart B). In the region of the Americas, for example, a total of 1,839 (15%) of the trials registered in 2023 were registered retrospectively (chart B). 

To explore the data further

• Hover the cursor on a data element of interest to see more information in a popup window (e.g. a regional segment from the year specific bars in chart A, or a point in a trend line for the number of trials with retrospective registration in a given year in chart B).
  -- For example, hovering on the segment of the bar for the Unknown region in 2022 (chart B) shows that 4,163 trials were registered in that year.
• To filter results by region, click a region from the key (chart A). Chart A will illustrate the number of trial registrations by year and chart B will display the trend line for the percent of trials with enrollment year preceding the registration year for that region.
• Hold the Ctrl key to select more than one region.
• Undo a selection by clicking ‘undo’ or ‘reset’ near the bottom of the page or by clicking the same element again.

Limitations of the data and analysis

• There are several gaps in the ICTRP data source which required data cleaning to uniformly classify data elements when possible. In some cases no information was available, e.g. unknown region and country grouping.
• The data presented in the ICTRP visualizations utilizes classifications that are not mutually exclusive. For example, a registered trial can recruit participants from multiple study sites, located in multiple countries and regions. The number of trials reported across the different visualizations is therefore not equivalent due to some duplication.
• The data is drawn from ICTRP data at the end of June 2024. This enables accurate reporting of data from 2023 to allow for some lag in data entry. This also means that 2024 data is inherently incomplete and is not indicative of the state of 2024.
• The analysis will be updated at regular time points but time lags with the scheduled updates by the data sources are inevitable. Accuracy and completeness of the information is the responsibility of the data source, see  terms and conditions of use.

Data sources

• WHO International Clinical Trials Registry Platform (ICTRP)

Previous versions

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