• epidemiologic studies
  • case-control studies
  • retrospective studies
  • cohort studies
  • longitudinal studies
  • follow-up studies
  • prospective studies
  • cross-sectional studies
  • seroepidemiologic studies
  • hiv seroprevalence
  • clinical trials
  • clinical trials, phase i
  • clinical trials, phase ii
  • clinical trials, phase iii
  • clinical trials, phase iv
  • controlled clinical trials
  • randomized controlled trials
  • multicenter studies
  • feasibility studies
  • intervention studies
  • pilot projects
  • sampling studies
  • twin studies