With few exceptions, much of sexual science builds upon data from opportunistic nonprobability samples of limited generalizability. Although probability-based studies are considered the gold standard in terms of generalizability, they are costly to apply to many of the hard-to-reach populations of interest to sexologists. The present article discusses recent conclusions by sampling experts that have relevance to sexual science that advocates for nonprobability methods. In this regard, we provide an overview of Internet sampling as a useful, cost-efficient, nonprobability sampling method of value to sex researchers conducting modeling work or clinical trials. We also argue that probability-based sampling methods may be more readily applied in sex research with hard-to-reach populations than is typically thought. In this context, we provide three case studies that utilize qualitative and quantitative techniques directed at reducing limitations in applying probability-based sampling to hard-to-reach populations: indigenous Peruvians, African American youth, and urban men who have sex with men (MSM). Recommendations are made with regard to presampling studies, adaptive and disproportionate sampling methods, and strategies that may be utilized in evaluating nonprobability and probability-based sampling methods.

We examined structural factors—social, political, economic, and environmental—that increase vulnerability to HIV among indigenous people in the Peruvian Amazon. Indigenous adults belonging to 12 different ethnic groups were purposively recruited in four Amazonian river ports and 16 indigenous villages. Qualitative data revealed a complex set of structural factors that give rise to environments of risk where health is constantly challenged. Ferryboats that cross Amazonian rivers are settings where unprotected sex—including transactional sex between passengers and boat crew and commercial sex work—often take place. Population mobility and mixing also occurs in settings like the river docks, mining sites, and other resource extraction camps, where heavy drinking and unprotected sex work are common. Multilevel, combination prevention strategies that integrate empirically based interventions with indigenous knowledge are urgently needed, not only to reduce vulnerability to HIV transmission, but also to eliminate the structural determinants of indigenous people’s health.

Men who have sex with men (MSM) have the highest HIV prevalence in Peru, yet they are underserved by traditional preventive programs. In Peru, the Internet and mobile phones have emerged as an effective and convenient tool to reach this population. From October 2010 to February 2011, we conducted eight focus groups with gay identified MSM (closeted and out-of-the-closet) and with self-identified heterosexual MSM in order to identify key features and preferences to be used to tailor culturally-appropriate messages that could be delivered through Internet and mobile phones to motivate MSM to get tested for HIV. Participants reported that in order to motivate HIV testing among MSM, interventions need to be based on motivational messages that encourage participants to overcome the fear of getting tested. Messages should increase the HIV risk perception (of participants who do not consider themselves at risk) by eliciting risky situations experienced by MSM. Messages should emphasize confidentiality, respect and the professionalism of the personnel conducting the counseling and testing. A thorough explanation of the process of HIV testing and the steps to follow after receiving the results should be provided. Messages should also contain information about the venue where the test will be conducted in terms of client characteristics, location, hours of operation and personnel. Finally, stigmatizing and stereotyping messages or images about “being gay” should not be included, as they act as deterrents for getting tested. Interventions aimed at motivating HIV testing among MSM should include motivational messages that reduce the fear of getting tested and increase the risk perception of participants. They should also market the venue where the testing will be conducted, the professionals who will perform the tests, and the type of tests available. Stigmatizing messages or images should be avoided.