What research method was used when a team assigned newborns to different care groups?

The correct answer is experimentation because this method involves the manipulation of variables to observe the effects of those manipulations. In the scenario described, assigning newborns to different care groups indicates that the researchers are intentionally controlling the environment or treatment that each group receives. This allows for a cause-and-effect analysis, as researchers can compare outcomes based on the specific interventions applied to each group.

In the context of psychology, experimentation is essential for determining whether changes in one variable directly result in changes in another. By using random assignment to different care groups, the researchers can minimize potential biases and ensure that any differences observed in the outcomes are likely due to the care received rather than external factors.

Surveys, case studies, and observational studies, while valuable research methods, do not involve the same degree of control over variables or manipulation of conditions to ascertain direct causal relationships. Surveys gather self-reported data, case studies focus on in-depth examination of a single subject or small group, and observational studies typically involve watching subjects in their natural environments without intervention. These approaches are useful for different research questions but do not provide the same level of evidence for causation that an experimental design does.