Panel Study of Income Dynamics (PSID)The PSID by the University of Michigan is the longest running longitudinal household survey (1968 - present) in the world. The study began with a nationally representative sample of over 18,000 individuals living in 5,000 families in the United States. Information on these individuals and their descendants has been collected continuously, including data covering employment, income, wealth, expenditures, health, marriage, childbearing, child development, philanthropy, education, and numerous other topics.