Rosenberg Molly, Pettifor Audrey, Twine Rhian, Hughes James P, Gomez-Olive F Xavier, Wagner Ryan G, Sulaimon Afolabi, Tollman Stephen, Selin Amanda, MacPhail Catherine, Kahn Kathleen
Department of Epidemiology and Biostatistics, Indiana University School of Public Health, Bloomington, Indiana, USA.
Department of Epidemiology, University of North Carolina, Chapel Hill, North Carolina, USA.
BMJ Open. 2018 Jan 10;8(1):e019167. doi: 10.1136/bmjopen-2017-019167.
We examined the potential influence of both sample selection effects and Hawthorne effects in the behavioural HIV Prevention Trial Network 068 study, designed to examine whether cash transfers conditional on school attendance reduce HIV acquisition in young South African women. We explored whether school enrolment among study participants differed from the underlying population, and whether differences existed at baseline (sample selection effect) or arose during study participation (Hawthorne effect).
We constructed a cohort of 3889 young women aged 11-20 years using data from the Agincourt Health and socio-Demographic Surveillance System. We compared school enrolment in 2011 (trial start) and 2015 (trial end) between those who did (n=1720) and did not (n=2169) enrol in the trial. To isolate the Hawthorne effect, we restricted the cohort to those enrolled in school in 2011.
In 2011, trial participants were already more likely to be enrolled in school (99%) compared with non-participants (93%). However, this association was attenuated with covariate adjustment (adjusted risk difference (aRD) (95% CI): 2.9 (- 0.7 to 6.5)). Restricting to those enrolled in school in 2011, trial participants were also more likely to be enrolled in school in 2015 (aRD (95% CI): 4.9 (1.5 to 8.3)). The strength of associations increased with age.
Trial participants across both study arms were more likely to be enrolled in school than non-participants. Our findings suggest that both sample selection and Hawthorne effects may have diminished the differences in school enrolment between study arms, a plausible explanation for the null trial findings. The Hawthorne-specific findings generate hypotheses for how to structure school retention interventions to prevent HIV.
我们在行为性HIV预防试验网络068研究中，考察了样本选择效应和霍桑效应的潜在影响。该研究旨在检验以入学为条件的现金转移支付是否能降低南非年轻女性的HIV感染率。我们探究了研究参与者的入学情况与潜在人群是否存在差异，以及这种差异是在基线时就存在（样本选择效应）还是在研究参与过程中出现（霍桑效应）。
我们利用阿金库尔健康与社会人口监测系统的数据，构建了一个由3889名11至20岁年轻女性组成的队列。我们比较了2011年（试验开始）和2015年（试验结束）时参与试验者（n = 1720）和未参与试验者（n = 2169）的入学情况。为了分离出霍桑效应，我们将队列限制为2011年入学的人群。
2011年，试验参与者入学的可能性已经高于未参与者（分别为99%和93%）。然而，经过协变量调整后，这种关联减弱了（调整风险差（aRD）（95%置信区间）：2.9（-0.7至6.5））。将范围限制在2011年入学的人群中发现，试验参与者在学校注册的可能性在2015年也更高（aRD（置信区间):(95%）：4.9（1.5至8.3））。关联强度随年龄增长而增加。
两个研究组中的试验参与者比未参与者更有可能入学。我们的研究结果表明，样本选择效应和霍桑效应可能都减小了研究组之间入学情况的差异，这可能是试验结果为阴性的一个合理原因。特定于霍桑效应的研究结果为如何构建防止HIV感染的学校留校干预措施提出了假设。
