Which of the following definitions applies to primary evidence?

Primary evidence refers to original research or direct evidence gathered through experiments, observations, or firsthand accounts. In this context, the definition of primary evidence is most accurately represented by an experiment designed to determine cause and effect. This type of evidence provides the most direct insights into a phenomenon by establishing a direct relationship between variables, allowing researchers to draw conclusions based on empirical data.

By conducting an experiment, researchers can control conditions and manipulate variables, thereby observing the effects in real time and providing concrete evidence that supports or challenges a hypothesis. This ability to establish causation is what distinguishes primary evidence from secondary sources or reviews, which analyze or summarize existing information rather than generating new data.

The other options represent forms of evidence that do not align with the direct nature of primary evidence. A case study involving multiple subjects is a method of aggregation and does not necessarily provide direct cause-and-effect data. A comprehensive review of secondary literature synthesizes findings from existing studies, while a preliminary survey of public opinion gathers information without experimental manipulation, both of which are not considered primary evidence.