Study Methodology

The Millennium Cohort Family Study is part of the larger Millennium Cohort Program (MCP), which is the first U.S. military population-wide research program to investigate the long-term health effects of military service among military personnel, their spouses, and children. The Family Study includes male and female spouses of active duty, Reserve, and National Guard personnel from all six branches (Army, Navy, Air Force, Space Force, Marine Corps, and Coast Guard) of the U.S. military. Military spouses are eligible to join the MCP Family Study if they are married to a service member invited to join the MCP as part of the Millennium Cohort Study (MCS) of service members.

Since it first began in 2001, the MCS has enrolled 5 panels of service members. The Family Study began about 10 years later and has enrolled two panels of military spouses. In 2011, the Family Study enrolled panel one, including almost 10,000 spouses, and in 2020 over 18,000 spouses were enrolled into panel two. When new panels are enrolled, participants are recruited using DoD service records in order to recruit a representative population of junior military personnel (2-5 years of service) and their spouses from across the Department of Defense. Participants volunteer to complete a self-report survey every three years for up to 21 years for spouses and 67 years for military members. Family Study spouses are followed even if their military partner separates from service or if their relationship status changes (i.e., separated, divorced, or widowed).