400 subjects will be enrolled through Respondent Driven Sampling method. The RDS methodology is based on long-chain recruitment whereby members of the target population participating in the study refer other members of the target population to the study. It is a modified form of snowball sampling which allows researchers to recruit highly-stigmatized groups who do not congregate in well-known places. RDS does not only provide a probabilistic method to reach the desired sample size, but also allows the research group to identify networks and the characteristics of those belonging to the networks.
Tasks will include:
1) analysis of the productivity of seeds and time-delay to achieve the desirable number of branches.
2) assessment of the field conditions (safety of field team members, confidentiality during the data collection)
3) choice of recruitment sites and procedures (number of subjects to be recruited by the seeds in order to limit individual influence on the sample, information on linkages between recruiters and recruits, size of participants' social networks for bias adjustment)
4) training of data collectors according to the protocol.
Partners will be in charge of monitoring and coaching data collectors. This will be part of the ongoing evaluation process, that could also include regular meetings with data collectors.
RDS methodology is implemented in Italy (Verona), Slovakia, Romania, Lithuania.