Final answer:
Longitudinal research is the most complex and beneficial research design for studying changes over time, as it involves repeatedly gathering data from the same subjects across an extended period.
Step-by-step explanation:
The most complex and beneficial way to study change over time in the field of social research is through longitudinal research. This type of research design involves collecting data from the same subjects repeatedly over a period of time. For instance, researchers might gather information on individual dietary habits at different stages of life, say at 20, 30, and 40 years of age, to observe changes and patterns. Longitudinal studies offer the advantage of observing how variables change over time, while also controlling for the cohort effect, since the same subjects are used throughout the study. Although this design can be resource-intensive and vulnerable to attrition, it remains one of the most powerful designs for understanding cause-and-effect relationships over time when compared to other methods such as cross-sectional research, archival research, or naturalistic observation.