Dr. Anderson 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 (for example, whimpering and pain cries), as well as caregiver responses (for example, holding and speaking). Dr. Anderson then chooses 50 participants in four different countries to be included in the study. What type of research design is she using