The Trans PULSE Data Set

2.2.1 Data Collection Overview

After launching in May 2009, 433 surveys were completed by trans persons who were at least 16 years old and residing in the province of Ontario, Canada. The surveys were made available online, via paper-copy and via telephone with assistance from a language interpreter. Data were collected through the use of a chain-referral sampling method known as Respondent Driven Sampling (RDS)71. Data collection progressed over one year, ending in May 2010.

2.2.2 Recruitment

Respondent driven sampling (RDS) was employed to the task of recruiting trans Ontarians to the Trans PULSE study because of the absence of a sampling frame for these populations. Having no sampling frame meant that there was no list or directory that identified and enumerated the members of the group; therefore no random sample could be drawn71,72,73,74,75,76,77. The incentive system and the use of social networks for recruitment purposes meant that RDS had a greater potential for reaching the “hidden” population sought by the research team78.

Overview of the RDS Procedure

RDS is a type of chain referral, or snowballing method that samples individuals through their personal

networks71,72,73. Other non-random, non-probability sampling methods are subject to selection bias because the probability of selection into the sample is unknown76. This is overcome in RDS through the collection of

information about the size of each participant’s peer network, which is then used to calculate the probability of selection within the network76. Using known network properties help to account for clustering effects76. In RDS,

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a few members of the target population, called “seeds” are recruited by members of the research team78. The seeds (representing the 0th recruitment wave) then initiate a chain-referral process by recruiting a set number of their peers (wave 1), who then recruit a set number of their peers (wave 2), and so on78. The seed refers their peer into the study by providing them with a coupon that has a unique serial number78. The potential recruit then chooses to participate or not. If an eligible peer enrolls in the study, his recruiter is reimbursed for their efforts78. Ideally, chain referral then continues for several waves of recruitment resulting in long recruitment chains76. Generally, chain referral is stopped when the target sample size is attained79, or when the sample reaches equilibrium with respect to the variables being measured78. This equilibrium is achieved when the sample distribution of key variables remains stable within 2% of the equilibrium distribution, even as more individuals are added to the sample76.

Trans PULSE and RDS

Recruitment for Trans PULSE began in 2009 with 16 seeds, representing the 0th wave of recruitment. These initial participants were members of Trans PULSE’s Community Engagement Team, who like other participants, met the eligibility requirements of the study, were well-connected in trans communities, were geographically dispersed, and were diverse with regard to income, age, ethnicity, and immigration status. These well-

connected individuals, who were knowledgeable of the trans communities, and who had interest in the goals of the study, were chosen in order to ensure adequate networking and effective penetration of the target

communities76. These seeds were given a limited number of coupons, in order to minimize the influence of the initial seeds on the final composition of the sample, thus reducing the potential for producing a sample biased by differential recruitment73,77,78. Essentially, limiting the number of coupons, “allow[ed] for an increase in the social distance between seeds, initial recruits, and later recruits”80 (p65). After, recruitment had been allowed to reach four or five waves, the Trans PULSE Steering Committee found it necessary to re-seed, in response to a slowing down of recruitment, and because some seeds had not sprouted (specifically, 2 seeds had not recruited others into the study). There were, thus, 38 seeds in total at the end of the project’s recruitment period in 2010. These recruited 433 people into the study. The entire sample, including the seeds, was used in this study.

Homophily

Homophily is the tendency for individuals to affiliate with others who are like themselves in terms of education, income, ethnicity, and general interests81. It is the “preference for connections to one's own group” and varies

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between -1 (completely heterophilous) and +1 (completely homophilous)82 (p32). According to Erickson83 this bias is introduced during seed selection and can be further compounded with each additional recruitment wave, with the final sample composition simply reflecting the characteristics of the initial seeds. However, according to Heckathorn72, with each successive wave of recruitment, the sample attains and maintains a stable composition, or equilibrium, that does not change even as more members enter into the sample, suggesting that the final composition would be the same regardless of the choice of initial seeds72. Bias, then, becomes progressively weaker with each wave until it is negligible73. When participants recruit three peers, as was done in the Trans PULSE recruitment method, this equilibrium can be reached within six recruitment waves73. The Trans PULSE sample was allowed to progress beyond 6 waves, with the longest chain reaching 10 waves of recruitment, and as was already discussed, the diverse seed choice further decreased the likelihood of obtaining a homophilous sample. Furthermore, RDSAT, our analysis tool, allows for control of homophily through the application of appropriate weighting80. Nevertheless, where homophily appears excessive, interpretations are made with caution. Homophily poses a threat to accuracy of analysis, because statistical power is much reduced when homophily is high. This is because if a sample is homophilous, then there is little difference between the status markers of participants in the sample, and, it therefore becomes difficult to detect differences between them.