Experimental research is defined as

• A. Describing existing conditions without interventions
• B. Measuring prevalence of a disease
• C. Analyzing historical data
• D. Comparing two or more conditions for the purpose of determining cause-and-effect relationships

Answer: (D)

Experimental research asks: does actively changing something produce a different outcome? It involves manipulating an independent variable (the intervention) and observing the resulting effect on a dependent variable, ideally with random assignment to different conditions and a control group. This setup is designed to isolate the impact of the intervention and establish cause-and-effect relationships, rather than just describing or measuring without manipulation.

The option that describes comparing two or more conditions to determine cause-and-effect relationships fits this idea because it explicitly seeks to establish causality by contrasting groups or scenarios under controlled differences. In contrast, describing existing conditions without intervention is descriptive, measuring prevalence is about how common something is at a moment in time (descriptive epidemiology or cross-sectional), and analyzing historical data involves looking back at past information, which often cannot prove causality due to lack of controlled manipulation and potential confounding.