Data Collection

Over the span of the COGA project, data has been collected in phases. For detailed information on each phase of the project, click on the headings.

Phase I: 1991-1998

  • 10,658 children (age 7+), adolescents, and adults from 2,246 families at 6 data collection sites across the country
  • Subjects completed interviews, questionnaires, EEG testing and provided DNA

Phase II: 1995 – 2005

  • 11,301 children, adolescents, and adults consisting of: a) Phase I subjects returning for 2nd assessment; b) new participants from Phase I families; c) Howard University subjects added to increase minority representation
  • Subjects given similar but updated Phase I assessment battery; cognitive tests added

Phase III: 2003 – 2005

  • 474 children, adolescents, and adults drawn from Phases I and II, most of whom were seen for a 5-year follow-up during this phase

Prospective Study: 2004 – 2019

  • Subjects aged 12 – 22 from original families and evaluated every two years
  • Assessments similar to those in Phase II, updated to target young age range

One-Year Pilot Study of Older Adults: 2016 – 2017

  • 2,174 subjects aged 50+ from Phases I and II who had not been seen for an average of 23 years
  • 706 subjects located and interviewed by telephone about physical & mental health and alcohol use/problems

Lifespan Phase: 2019 – 2024

  • Two groups: a) Prospective subjects aged 30+; and b) Phase I/II subjects aged 50+
  • Assessments updated from Prospective protocol, emphasizing middle and later years of life


  • Interviews conducted by telephone March – July 2020; questionnaires mailed or completed on the Web; EEG and neuropsychological tests suspended
  • Beginning August 2020, subjects begin returning for in-person laboratory evaluations at some sites, as conditions allow; interviews and questionnaires continue to be administered largely remotely (June, 2022)