Parlez-vous HIV study lingo? Some common research terms:

Cohort—A group being studied. Notable cohorts include the Multicenter AIDS Cohort Study (MACS), with more than 5,000 gay and bisexual male HIVers across America, and the Women’s Interagency HIV Study (WIHS), involving more than 2,500 women.

Bias—A flaw that changes the results. Example: A “selection bias” skews data because of unrepresentative subjects—only seeking participants from the back rooms of sex clubs, say, to study gay men’s safer-sex practices.

Blinded—Participants don’t know if they’re getting the treatment drug or the placebo (or a new combo vs. an older one). Researchers can be blinded, too, not knowing which treatment which patients get. Patients and researchers both in the dark? The study is double-blinded.