The war in Syria belongs to the most dramatic emergencies in the last decades forcing a large number of people to seek refuge in other countries. Information on health-related aspects and special needs of Syrian migrants is urgently required, especially in countries hosting a considerable number of Syrians like Germany. However, data is scarce and as survey response using traditional sampling methods is usually low, one of the biggest challenges is finding appropriate sampling strategies to obtain representative results. In order to increase survey response in hard-to-reach populations, new methods were developed. One of them is respondent-driven sampling (RDS), a network sampling technique that starts with a small convenience sample of the target population (“seeds”) which is asked to complete the survey. All participants should then invite a limited number of their contacts (“peer-recruited participants”) who are also members of the target population to participate in the survey. In Germany, however, RDS has hardly been used for sampling migrant populations. Therefore, we aimed to assess if respondent-driven sampling (RDS) is a better approach to recruit Syrian migrants for health research than random sampling via the population registry.

A cross-sectional study was conducted in Munich, Germany between April and June 2017 inviting adults (18+ years) born in Syria to answer an online questionnaire asking for sociodemographic and health-related information. The participants were recruited using two sampling strategies: random sampling via the population registry (PR) and respondent-driven sampling (RDS). The two study populations were compared to the total sample drawn from the population registry with respect to gender and citizenship. In addition, the two study populations were compared to each other regarding self-reported health status, healthcare utilization, lifestyle factors, social network size, and acculturation.

Of 374 persons randomly drawn from the population registry, 49 individuals answered the questionnaire completely (response: 13.1%) while via RDS 195 participants were recruited by 16 seeds. More persons possessed German citizenship in the total PR sample (20.5%, 95% CI: 16.5–24.5%) and in the PR study population (28.6%, 95% CI: 15.5–41.7%) than in the RDS study population (0.5%, 95% CI: −0.1 to 1.1%). Participants recruited via the population registry were older, smoked less, reported more often to hold a university degree, and indicated a higher prevalence of chronic diseases, more frequent healthcare utilization, higher scores of acculturation as well as a larger social network compared to the study population obtained via RDS.

As expected, response was very low among the random sample drawn from the population registry while a larger number of participants were recruited via RDS using only 16 seeds. In addition, the two recruitment strategies led to study populations with substantially different characteristics indicating selection bias in either method. These findings provide valuable information for upcoming population-based studies investigating health-related aspects in migrants indicating that mixed sampling approaches combining various recruitment strategies may enhance representativeness.