Final answer:
The study involves (2) the random assignment of participants, an essential technique in experimental research for ensuring equality in group assignment and validity of results.
Step-by-step explanation:
When participants in an experiment have an equal chance of being assigned to the experimental or control groups, this signifies the use of random assignment. Random assignment is a technique ensuring that each participant is equally likely to be placed in any group, aiming to balance out any potential preexisting differences among participants. Such an approach is fundamental in experimental designs to test cause-and-effect relationships, allowing researchers to attribute differences in outcomes directly to the manipulation of the independent variable.
Therefore, the answer to the student’s question is (2) the random assignment of participants. This method helps to prevent systematic differences between groups, leading to more reliable and valid results. Random assignment is particularly crucial in establishing causal links between variables in experimental research.