Percent of clinical trials with enrollment year preceding registration year (1999-2017)

Published: January 2018

The analysis includes data on all retrospective trial registrations in the WHO International Clinical Trials Registry Platform (ICTRP) for the period 1999–2017. Retrospective registration is 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

The top chart shows trial registration for the period 1999–2017 by year, color coded by WHO region. The bottom chart shows the percent of trials with the enrollment year proceeding 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 1999–2017. Trials are predominantly registered in three WHO regions: The Americas, Europe and the Western Pacific. The WHO region in which fewest trials are registered in ICTRP is Africa, although numbers of registered trials in Africa are increasing.
  • Although, in 2017, the majority of trials are registered within one year of first enrollment, ranging from 79% in the Western Pacific to 61% in the South-East Asia and Eastern Mediterranean regions, a considerable number still remain unregistered after one year. In Europe, for example, a total of 2,452 (24%) of the trials registered in 2017 were registered retrospectively.

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 the top chart, or a point in a trend line for number of trials with retrospective registration in a given year in the bottom chart).
    -- For example, hovering on the segment of the bar for the Western Pacific region in 2017 (top chart) shows that 13,748 trials were registered in that year.
  • To filter results by region, click a region from the key (top chart). The top chart will illustrate the number of trial registrations by year for that region. The bottom chart 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 county 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.