What type of research assesses genetic links among family members?

The correct choice is the family study, which is specifically designed to investigate genetic links by examining the traits and behaviors of family members. This type of research allows scientists to analyze how certain characteristics, including psychological traits and disorders, are inherited within families. By comparing the prevalence of these traits in family members, researchers can determine the degree to which genetics plays a role in their development.

In a family study, researchers often evaluate multiple generations, assessing correlations between the characteristics of parents and their offspring, as well as among siblings. This methodology provides valuable insights into heritability, as well as the potential influence of environmental factors that family members might share.

The other types of studies mentioned serve different research purposes. Longitudinal studies observe the same subjects over a long period to track changes and developments, cross-sectional studies analyze data from different subjects at a single point in time for a snapshot view, and case studies provide an in-depth examination of a single individual or group. While these methods can contribute to understanding behavioral patterns, they do not specifically focus on genetic relationships within families like family studies do.