Final answer:
The statement that developmental theories differ from personal theories by using systematic, scientific methods is true. Developmental psychology research methods include naturalistic observations and case studies, and they adhere to the scientific method.
Step-by-step explanation:
Developmental theories differ from personal theories of human development in that they utilize systematic, scientific methods of investigation. This is a true statement. Developmental psychologists employ research methods such as naturalistic observations, case studies, surveys, and experiments to understand the developmental changes that individuals undergo mentally and physically over time. These methods are part of the scientific method, which is a structured approach to research involving specific steps like developing hypotheses, conducting experiments, and making careful observations. A scientific theory, in contrast to a personal theory, is a well-tested and confirmed explanation for a set of observations or phenomena that is the foundation of scientific knowledge.