Unpublished Studies Report More Adverse Events

Reporting of Adverse Events in Published and Unpublished Studies of Health Care Interventions: A Systematic Review – September 20, 2016

Adverse events (AEs) are harmful or undesirable outcomes that occur during or after the use of a drug or intervention but are not necessarily caused by it.

Serious or important adverse events may occur rarely and, consequently, systematic reviews and meta-analyses that synthesize harms data from numerous sources (potentially involving both published and unpublished datasets) can provide greater insights.  

The Database of Abstracts of Reviews of Effects (DARE) includes 104 reviews of adverse events published in 2010 and 344 in 2014. 

We have previously noted that systematic reviewers, in line with current guidance, are increasingly conducting broader searches that include

  • unpublished sources, such as theses and dissertations, 
  • conference proceedings,
  • trial registries, and
  • information provided by authors or industry.

This is despite the difficulties in obtaining and incorporating unpublished data into systematic reviews.

Serious concerns have emerged regarding publication bias or selective omission of outcomes data, whereby negative results are less likely to be published than positive results. This has important implications for evaluations of adverse events because conclusions based on only published studies may not present a true picture of the number and range of the events.

The additional issue of poor reporting of harms in journal articles has also been repeatedly highlighted.

The problem of missing or unavailable data is currently in the spotlight because of campaigns such as AllTrials (www.alltrials.net), the release of results in trial registries (through the 2007 Food and Drug Administration Amendment Act), and increased access to clinical study reports (CSRs). 

In addition, reporting discrepancies, including omission of information, have recently been identified between studies published as journal articles and the corresponding unpublished data.

These emerging concerns indicate that publication and reporting biases may pose serious threats to the validity of systematic reviews of adverse events. Hence, we aimed to estimate the potential impact of additional data sources and the extent of unpublished information when conducting syntheses of adverse events.

This present methodological review updates previous work by focusing on quantifying the amount of unpublished adverse events data as compared to published data, and assessing the potential impact of including unpublished adverse events data on the results of systematic reviews.


The 28 studies included in our review give an indication as to the amount of data on adverse events that would have been missed if unpublished data were not included in assessments.

This is in terms of

  • the number of adverse events,
  • the types of adverse events, and
  • the risk ratios of adverse events.

We identified serious concerns about the substantial amount of unpublished adverse events data that may be difficult to access or “hidden” from health care workers and members of the public.

Incomplete reporting of adverse events within published studies was a consistent finding across all the methodological evaluations that we reviewed.

Our findings suggest that it will not be possible to develop a complete understanding of the harms of an intervention unless urgent steps are taken to facilitate access to unpublished data.

The extent of “hidden” data has important implications for clinicians and patients who may have to rely on (incomplete) published data when making evidence-based decisions on benefit versus harms.

Our findings suggest that poor reporting of harms data, selective outcome reporting, and publication bias are very serious threats to the validity of systematic reviews and meta-analyses of harms.

In support of this, there are case examples of systematic reviews that arrived at a very different conclusion once unpublished data were incorporated into the analysis. 

Although the process of searching for unpublished data and/or studies can be resource-intensive—requiring, for example, contact with industry, experts, and authors and searches of specialist databases such as OpenGrey, Proquest Dissertations and Theses, conference databases, or websites and trial registries—we strongly recommend that reviews of harms make every effort to obtain unpublished trial data. In addition, review authors should aim to specify the number of studies and participants for which adverse outcome data were unavailable for analysis. The overall evidence should be graded downwards in instances where substantial amounts of unpublished data were not accessible.

Our review demonstrates the urgent need to progress towards full disclosure and unrestricted access to information from clinical trials.

This is in line with campaigns such as AllTrials, which are calling for all trials to be registered and the full methods and results to be reported.

We are starting to see major improvements, however, in the availability of unpublished data based on initiatives of

  • the European Medicines Agency (EMA),
  • European law (the Clinical Trial Regulation),
  • the FDA Amendments Act of 2007—which requires submission of trial results to registries—and
  • pressure from Cochrane to fully implement such policies

Journal editors and readers of systematic reviews should be aware that a tendency to overestimate benefit and underestimate harm in published papers can potentially result in misleading conclusions and recommendations

the available examples clearly demonstrate that availability of unpublished data leads to a substantially larger number of trials and participants in the meta-analyses.

We also found that the inclusion of unpublished data often leads to more precise risk estimates (with narrower 95% confidence intervals), thus representing higher evidence strength according to the GRADE (Grades of Recommendation, Assessment, Development and Evaluation) classification, in which strength of evidence is downgraded if there is imprecision

In conclusion, therefore, there is strong evidence that substantially more information on adverse events is available from unpublished than from published data sources and that higher numbers of adverse events are reported in the unpublished than the published version of the same studies.

The extent of “hidden” or “missing” data prevents researchers, clinicians, and patients from gaining a full understanding of harm, and this may lead to incomplete or erroneous judgements on the perceived benefit to harm profile of an intervention.

Authors of systematic reviews of adverse events should attempt to include unpublished data to gain a more complete picture of the adverse events, particularly in the case of rare adverse events. In turn, we call for urgent policy action to make all adverse events data readily accessible to the public in a full, unrestricted manner.

Copyright: © 2016 Golder et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use,
Data Availability: All data are within the paper and its Supporting Information files distribution, and reproduction in any medium, provided the original author and source are credited.

2 thoughts on “Unpublished Studies Report More Adverse Events

  1. Kahjy C

    This really should have been a problem years ago. This deliberate and pervasive “withholding” of negative results has led to this current Confusion. The Pharma Industry alone, with their unlimited funds made a lot of money. That is at the root of this. They found it pretty easy, since any Researcher in a Position to notice would either be shouted down, or their work will be buried. There are not many “Independent” Researchers, Government Statisticians or Academics anymore.

    Liked by 1 person

    1. Zyp Czyk Post author

      When our whole society is run under the assumption that profit is more important than citizen welfare, no one can be trusted to honestly pursue anything else.



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