What constitutes a "clinical trial"? Until recent years, this term was widely interpreted as referring only to randomized clinical trials. However, in 2015 the National Institutes of Health adopted a broader interpretation of this term, and began using the following description to define a clinical trial:

A research study in which one or more human participants are prospectively assigned to one or more interventions (which may include placebo or other control) to evaluate the effects of those interventions on health-related biomedical or behavioral outcomes.1

The way a clinical trial is defined is of particular relevance for journals, like the Journal of Neurologic Physical Therapy (JNPT), that publish manuscripts related to the outcomes of clinical trials. As with the use of standardized reporting guidelines,2 best practices for reporting of clinical trials require that these studies be registered3 so that details about essential elements of the study are publicly available to promote transparency in reporting. As noted in theJNPTInstructions for Authors, articles submitted through December 31, 2019, trials may be registered retrospectively; however, beginning in January 2020 clinical trials must be registered prospectively.

Since reputable rehabilitation journals require that clinical trials be registered the definition of a clinical trial is important, and the majority of journals use the NIH definition as a guide. In early 2018, in response to requests for clarification, the NIH published an updated series of cases that were intended to clarify the types of studies that meet the definition of a clinical trial.4 These cases describe studies wherein the answer to the following 4 questions is "yes," indicating that the study is a clinical trial: (1) Does the study involve human participants? (2) Are the participants prospectively assigned to an intervention (this applies to quasi-experimental single-group pre-post studies as well as randomized studies)? (3) Is the study designed to evaluate the effect of the intervention on the participants? (4) Is the effect being evaluated a health-related biomedical or behavioral outcome?

Beyond promoting transparency in reporting, registration of clinical trial through registries such a http://clinicaltrials.gov represents a valuable component of dissemination, ensuring that information about ongoing studies is available to persons who may be interested in participating. Likewise, registration helps prevent duplication of studies, and is a pragmatic way of acquainting researchers with various study designs. Readers, authors, and reviewers alike will find it valuable and informative to check out the NIH clinical trial case studies4 to learn about the many types of studies that fall under the umbrella of clinical trials.

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