Abstract
Information on transgender people's health, and especially their experiences of aging, is lacking, including from major longitudinal studies of aging like the Health and Retirement Study and its sister studies in the Gateway to Global Aging Data project. This paper surveys the state of gender data collection among major longitudinal studies and finds that all but one fail to collect adequate information on participants' gender to determine participants' gender identities. It identifies the unique challenges that population-wide longitudinal data collection poses to current best practices for identifying transgender survey participants and proposes a modified "two-question model": one question for sex assigned at birth and a second for gender identity, both of which offer 3 responses.