Reference individuals are highlighted in red, and panels A) first degree, B) second degree, C) third degree and D) random network members are highlighted in green. In panel A, individual e’s first degree network consists of network members directly connected to individual e: network member c (e’s recruiter) and network members h, i and j (the individuals recruited by e). In panel B, the second degree network consists of individuals two connections away from individual e. In panel C, the third degree network consists of individuals three connections away from individual e. In panel D, a random network was generated by randomly assigning respondents to different locations within the original RDS referral recruitment structure. Individual e’s position has shifted and new network members include individuals b, u, o and x.