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Previously published at www.cmaj.ca
Observational studies form an important part of the medical evidence base, particularly for assessing rare adverse events and long-term effectiveness of medications and devices.1 However, observational studies, like interventional studies (clinical trials), are subject to publication bias and reporting bias.2-4 Registration of clinical trials is a widely recognized tool for facilitating complete public reporting.5 Registration of observational studies has received less attention, although interest is growing.6-8 Because existing registries (e.g., ClinicalTrials.gov) accommodate observational studies, and the rationale and benefits of registration are similar, we ask the scientific community and other stakeholders to consider the systematic, prospective registration of observational studies.
Why register observational studies?
Much of the rationale for the prospective registration of clinical trials9 applies to the registration of observational studies (Table 1).7 For example, observational studies in which researchers acquire data directly from human participants entail ethical obligations to participants, even though such research generally involves less risk than interventional studies. 10 These obligations include oversight by ethical review boards, informed consent, and public release of the study findings to advance biomedical knowledge. As with clinical trials, incomplete reporting of observational studies has been documented. 3 Some researchers suggest that observational studies are also at increased risk for publication bias or other types of bias, including misrepresentation of prespecified analyses or phenotype definitions.2,4 Such biases are a concern because they undermine the validity of observational studies, which are an important component of the medical evidence base in areas of public health, such as detection of rare adverse events.1,16
Observational studies of medications and devices are playing a more visible role at the United States Food and Drug Administration (FDA) (Table 2). For instance, the FDA posted an "Early communication about an ongoing safety review"18 in response to a published observational study associating abacavir and didanosine with an increased risk of cardiovascular and cerebrovascular events.19 The authors of the study noted that, although a randomized controlled trial is necessary to show a causal association, such a trial design is "unlikely to be feasible," given that it would require more than 10 000 participants to be followed for at least two years. In addition, there may be ethical concerns in conducting a randomized controlled trial if harms are expected. Given that...