This document discusses different methods and approaches used to study human development, including observational methods, experimental methods, and longitudinal, cross-sectional, and cross-cultural approaches. The cross-sectional approach examines groups of different ages at one time to compare developmental levels. The longitudinal approach observes the same group over an extended period of time to study individual patterns of change. The cross-cultural approach compares customs, beliefs, and behaviors across multiple cultures to understand cultural influences on human behavior.