Final answer:
The term referring to the demonstration of the efficacy of an experimental intervention through single subject research designs is a 'controlled experiment'. In these experiments, causality is established between the independent and dependent variables under controlled conditions to validate the study's conclusions.
Step-by-step explanation:
The term used to describe the use of single subject research designs to demonstrate a functional relation, or a believable demonstration of the efficacy of an intervention, is known as a controlled experiment. In a controlled experiment, researchers manipulate one variable (the independent variable) to observe its effect on another variable (the dependent variable) while controlling for confounding variables.
This design often includes a control group that does not receive the experimental manipulation, ensuring that any observed effects can be attributed to the independent variable and not to other factors.
One key feature of controlled experiments is demonstrating causality, which means establishing a cause-and-effect relationship between variables. Proper experimental design is crucial for the validity of the conclusions drawn from the research. This may involve methods such as random assignment to treatment groups, using double-blind procedures, and ensuring the control group receives a placebo treatment.