Which of the following is an example of a primary source?

A primary source is defined as an original work that provides firsthand evidence or direct information about a subject. In this context, a journal article reporting on an original study is a prime example of a primary source because it presents original research findings, methodologies, and data collected by the authors. This allows readers to assess the research design, analyze results, and draw their conclusions based on the evidence provided directly from the source itself.

In contrast, a published commentary on another study or a textbook of nursing theories would be considered secondary sources, as they summarize and interpret existing research rather than present new findings. Similarly, a summary of existing research findings consolidates results from multiple studies but does not present original data or analysis. Therefore, while these alternatives may be useful for gaining insights, they do not qualify as primary sources like the journal article does.