Study design, population and study sites: This is a cross-sectional study conducted to determine the SRH needs of SIYPs in two states in southwestern Nigeria. The two States – Lagos and Osun -- were selected based on their level of industrialization. Lagos is an industrialized cosmopolitan state, while Osun is less industrialized. Data were collected in January to February, 2019.
The study participants were male and female adolescents aged 10 to 24 years, living ‘on’ and ‘of’ the street. At each study location, places where SIYPs congregate in large numbers, such as major streets, market places, and motor-parks, were identified through mapping conducted by the research team and officials of the State Ministry of Health. These locations were grouped as clusters. The clusters in Lagos State were Bariga and Ajah, and those for Osun State were Oke-Baale, Olaiya and Sabo.
Sample size: The determination of sample size for this study was guided by Turner , who recommended estimates to derive sample size for surveys on orphaned and vulnerable children (OVC) in homeless situations. Because of unavailability of data to generate a prevalence rate of OVC in the proposed study environment, the suggested minimum sample size of 800 to 1000 was adopted, and 1505 street-involved young people were enrolled in this study.
Study recruitment procedure: After community engagement, the study participants were recruited by use of respondent-driven sampling and time-location sampling methods [22,23]. The respondent-driven sampling method developed by Heckathorn  is a sampling process whereby participants recruit their peers in hard-to-reach populations . In this study, the first ten seeds recruited through the respondent-driven sampling were given a labelled tag with generated identity numbers. After their enrollment, the seeds were given two additional tags to recruit friends/peers. Each referred respondent was checked for eligibility, enrolled, and interviewed once the eligibility criteria were met. The eligibility criteria were age 10-24 years, living ‘on’ or ‘of’ the street in Lagos or Osun State, and stable mental status.
Recruitment of study participants through respondent-driven sampling was slow, as there were boundaries within street groups and low density of social networks. Thus, the research team adopted time-location sampling to recruit the target population at specific times, days, and venues where SIYP gather . To limit selection bias with this method, we selected venue-day-time options with likely large turnouts of SIYP for the recruitment of participants.
Through the respondent-driven sampling, 34 seeds were recruited, and 465 coupons were given out over six recruitment waves within five days; only 120 respondents were recruited and interviewed through this method. In contrast, the time-location sampling method resulted in 1800 coupons given and 1385 respondents recruited and interviewed [See Supplementary File 1 for study recruitment characteristics].
The questionnaire was administered in a place that the respondent identified to be most comfortable for responding to questions. Data were collected by the field worker electronically with REDcap - a secure web application used to build and manage online surveys/databases. The REDcap app was installed on tablets for offline use, and all data collected were uploaded to the secured website at the end of each day.
Study instrument: The research instrument was adapted from the “Illustrative Questionnaire for Interview-Surveys with Young People,” designed by Cleland for the World Health Organisation . The content of the questionnaire was revised by two experts in SRH to address the study objectives and fit within the Nigerian cultural context. The revised questionnaire was pre-tested with 20 selected SIYPs at two locations besides the study sites (Ile-Ife and Ibadan) to ascertain the clarity and conciseness of the questions. The tool was revised for language and procedural clarity, then translated into the local dialect (Yoruba) for respondents who do not understand English language. The questions were closed-ended, making data entry and analysis possible in English. Field workers who speak the other national languages - Ibo and Hausa – had access to interpreted key concepts in the questionnaire in line with the methodology used for national health surveys conducted in Nigeria .
Measurement of variables: The explanatory variable in this study was ‘knowledge of SRH’ measured by (i) knowledge of modern contraceptives and (ii) access to SRH information. A knowledge of modern contraceptives was deduced from responses to a question asked from respondents - “do you know of any of these methods which men and women can use to prevent pregnancy?” There were seven response options: (i) injection, (ii) condom, (iii) emergency contraception, (iv) traditional method, (v) withdrawal method, (vi) safe period and (vii) periodic abstinence. Options i-iii were recoded as ‘1’, implying knowledge of modern method of contraception, and ‘0’. no knowledge of modern contraception. Further, respondents were asked if they ‘ever attended/or were given a talk on SRH’; a positive response was assigned “1”, and otherwise “0”. The question was limited to information on SRH learned through talks since most SIYPS likely have restricted access to other sources of information, such as electronic media and social media. The respondents were also asked to state the contraceptive method they used at last sexual activity by self or partner.
The variables adjusted for in this study were selected background characteristics of respondents: age [10-14, 15-19, 20-24 years], level of education [none, primary, secondary], and employment status [not working, working]. The outcome variable was ‘sexual risk behavior’ proxied by three variables: (i) inconsistent use of condom, (ii) multiple sexual partners; and (iii) transactional sex. Both male and female respondents who were sexually active were asked if they used condom at the last sexual activity. An affirmative answer was assigned “1”, and a negative answer was assigned “0”. Respondents were also asked the number of sex partners they currently have. Those who responded that they had one were assigned “1”, while those who had more than one sex partner were assigned “0”. Two questions were asked to probe about transactional sex: “have you ever paid or exchanged gift for sex?” and “have you ever been paid or receive gift in exchange for sex?” An affirmative answer to either of the questions was assigned “1”, and a negative answer was assigned “0”.
Analysis: Data analysis was conducted with Stata SE 15.1 (Stata Corporation, College Station, Texas). The univariate analysis was conducted to determine the percentage distribution of participants by age in grouped years [10-14, 15-19, 20-24], sex, educational level, employment status, knowledge of modern contraception, and access to SRH information. Bivariate analysis was conducted to test associations between the explanatory and outcome variables by use of Pearson chi-square test. The inferential analysis was conducted with logistic regression to determine the risk indicators for the outcome variables by sex. Two models guided the regression analysis: The first model regressed each of the outcomes against the explanatory variables, while the second model adjusted for confounders (age, education level, and work status).
Based on the Pearson chi-square significant association test, we set the p-value cut-off point at 0.20 (p <0.20) for the inclusion of confounders in the regression model. The Hosmer-Lemeshow goodness-of-fit test was conducted to ascertain that all study variables fulfilled the underlying assumption of a univariate regression. Statistical significance was considered at p-value less or equal to 0.05.