A researcher is interested in determining if infant crying and caretaker responses are different in economically developed and developing nations. She trains her research assistants to watch and record babies' behaviors in 3-minute increments, including variations in crying (e.g., whimpering and pain cries), as well as caregiver responses (e.g., holding and speaking). The researcher then chooses 50 participants in four different countries to be included in the study. What type of research design is she using?

Naturalistic observation: In scientific or psychological research, the term naturalistic observation is defined as one of the research methods in which the researcher or the experimenter tends to study and observe the interested participants or subjects into their natural surroundings. The researcher or the experiments makes an effort to note everything they watch and notice about the participants or subjects being studied.

In naturalistic observation, there's a great chance of the results to be biased as the researcher or the experimenter makes results based only on his or her observation i.e, it lacks scientific approval.

In the question above, the researcher is using naturalistic observation.