Table 1 describes the characteristics of the study samples in Tirana and St. Petersburg. The sample in Tirana consists predominately of male IDUs, with only 14 female IDUs recruited for the survey. This contrasts substantially from the sample in St. Petersburg, where more females were represented compared to Tirana, with 36% being female and 64% being male.
In Tirana, the majority had completed at least middle school (eight classes), with a third of the sample completing middle school and a third completing high school (12 classes). Only 7% in Tirana had completed university. In St. Petersburg, the majority (84%) had completed either secondary or vocational education, and 16% had completed university. In Tirana, the sample was comprised of young IDUs with 38% between 15 and 22 years of age and 74% below 27 years of age. The St. Petersburg study included an older IDU population, with over half of participants 28 years of age or older and only 11% between 15 and 22 years of age. In St. Petersburg, males were slightly older than females; a much higher proportion of males were 28 years of age or older (66 vs 26% of females; data not shown).
The majorities of the samples are unmarried (85% in Tirana and 82% in St. Petersburg). In Tirana, the majority also did not live with a sex partner (65%), while another 20% were unmarried but living with a sexual partner. A higher proportion of IDUs in Russia reported being unmarried but living with a sex partner (33%).
As a part of RDS methodology, respondents were asked about the size of their personal networks. Specifically, participants were asked how many people they know personally who used injecting drugs (i.e., “you know who they are, they know who you are, you have seen them in the last six months”).
In Tirana, male IDUs reported a larger average personal network size than female IDUs. In contrast, in St. Petersburg, females had a larger average personal network size than males (20 vs 17, respectively).
The pattern of network size by age is again very different between IDUs in Tirana and St. Petersburg. In Tirana, network size increases with age (from 16 among the youngest age group to 21 in the oldest age group), whereas in St. Petersburg, network size decreases with age (from 25 in the youngest age group to 15 in the oldest age group). The same trend and differences between the two cities is observed with regard to education, which is likely due to the collinearity between age and education.
Similarly, in Tirana, there was a trend of increasing network size with increasing duration of injection drug use. However, in St. Petersburg, the network size was larger for recent initiates and long-term injectors compared to those who injected for 1–5 years (Table 2).
Table 3 represents the recruitment patterns of IDUs in Tirana and St. Petersburg with respect to sex, age and length of injection. RDS provides the opportunity to learn about the degree to which people tend to affiliate with others sharing their same characteristics. In Tirana, the gender affiliation patterns demonstrate a strong heterophily in women, whereby women recruited only men (H = −1.00), while men recruited women 7% of the time (H = 0.16; this is probably due to the small number of women in the Tirana sample, with only 14 women participating). From a possible 28 coupons given to these women, 16 coupons were returned (57%). In contrast, the gender affiliation patterns of IDUs in St. Petersburg reflects neither strong homophily nor heterophily. Both males and females recruited males about the same percentage of times (63 and 57%, respectively). The heterophily index in males was −0.02 and homophily index was 0.12 for females.
The affiliation patterns of age recruiting relations in IDUs in Tirana reflects neither homophily nor heterophily. The homophily indices were 0.02 for the younger (15–22 years), 0.05 for the medium age (23–27 years) categories, and 0.09 for the older age group (≥28 years). As can be seen, both youngest and the oldest age categories recruited the medium age group approximately one-third of the time. Further, both the youngest and the medium age groups equally recruited the oldest age group (approximately 23–29% of the time). Lastly, the medium and the oldest age groups recruited the youngest group with equal vigor at about one-third of the time.
Among IDUs in St. Petersburg, the affiliation patterns of age relations reflect neither homophily nor heterophily. The homophily indices were −0.03 for both the younger (15–22 years) and the medium age (23–27 years) categories, and −0.15 for the older age group (≥28 years).
In Tirana, as with the relations by age, the affiliation patterns of relations based on duration of injection drug use reflects neither homophily nor heterophily. The homophily indices were 0.09 for new injectors (i.e., <1 year of injection experience), −0.10 for the mid-term users (1–5 years), and 0.09 for the longer-term injectors (>5 years). New users were recruited the least by the mid- and longer-term injectors (8 and 4%, respectively), and both the new and longer term injectors recruited mid-term injectors (64 and 65%, respectively).
In St. Petersburg, however, the affiliation patterns of relationships by duration of injection drug use differed between new injectors and longer-term injectors. The group of new injectors was completely heterophilous (H = −1.0), reflecting a lack of in-group ties. However, both mid-term and longer-term injectors exhibited neither heterophily nor homophily (H = −0.07 and H = 0.05, respectively).