Percent of trials with enrollment year preceding registration year (1999-2021)

Published: February 2022

The analysis includes data on all retrospective trial registrations reported in the WHO International Clinical Trials Registry Platform (ICTRP) for the period 1999–2021. 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: 

Number of clinical trials by year, country, WHO region and income group

Number of clinical trial registrations by year, location, disease and phase of development

What you see | Scope and limitations | Data sources |  Current version

What you see

Chart A shows the trial registration for the period 1999–2021 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, although in 2021, a decrease is noticed in some regions, notably in Western Pacific region. 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 2021, the majority of trials are registered within one year of first enrollment, ranging from 93% in South-East Asia region to 73% in the Eastern Mediterranean region, a considerable number of trials remain unregistered after one year (hover over the point for the year 2021 on the line representing the region in chart B and subtract the displayed % in the popup from 100%). In the region of the Americas, for example, a total of 1,830 (17%) of the trials registered in 2021 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 2021 (chart B) shows that 4,520 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 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.