RESUMEN
Empirical gay, lesbian, bisexual, and transgender (GLBT) research has passed through three stages. Transitions between stages have been caused by an interaction of empirical research and institutional policies. The first period is from the late 1800s up to 1972, when research focused on categorizing homosexuality as a disease, treatments for homosexuality, and then research refuting the disease model. The second period ran from 1972 to approximately 1990, when researchers began to apply the disease model not to GLBT persons, but rather to those having negative attitudes toward homosexuality (homophobia), and researchers began to look at what it was like to be a GLBT person from GLBT persons' perspectives. The third period began in the early 1990s and continues today, when researchers focus on institutions, particularly action research aimed at changing institutions.