Background How much a randomized controlled trial (RCT) sample is representative of or differs from its source population is a challenging question, with major implications for generalizability of results. It is particularly crucial for freely-available web-based interventions tested in RCTs since they are designed to reach broad populations and could increase health disparities if they fail to reach the more vulnerable individuals. We assessed the representativeness of a sample of participants in a primary/secondary prevention web-based brief intervention RCT in relation to its source population. Then we compared those recruited to those not recruited in the RCT. Methods There is a mandatory army recruitment process in Switzerland at age 19 for men. Between August 2010 and July 2011, 12,564 men (source population) attended two recruitment centers and were asked to answer a screening questionnaire on alcohol use. Among 11,819 (94.1%) who completed it, 7027 (59.5%) agreed to participate in a longitudinal cohort study with regular assessments. In 2012, these participants were invited to a web-based brief intervention RCT. Participation was not dependent on the presence or quantity of alcohol use. We assessed the representativeness of the RCT sample in relation to the source population and compared participants recruited/not recruited in the RCT with respect to education level and alcohol use. Results The RCT sample differed from the source population: individuals 20 and over were significantly less represented (34.3% vs 37.9%, p = 0.006), as were those with lower education level (58.6% vs 63.0%, p = 0.0009). The prevalence of any alcohol use was higher in the RCT population (92.3% vs 90.6%, p = 0.03) but unhealthy alcohol use was less represented (37.1% vs 43.2%, p < 0.0001). Differences on alcohol use measures and education were similarly found when those recruited in the RCT were compared to those who were not, including in a multivariable model, showing independent associations between less unhealthy alcohol use and higher education and recruitment in the RCT. Conclusions RCT participants differed from other members of the source population, with those participating in the RCT having higher prevalence of any alcohol use but lower levels of consumption and lower prevalence of indicators of unhealthy alcohol use. Individuals with higher education were overrepresented in the RCT sample. Selection bias may exist at both ends of the drinking spectrum and individuals with some indicators of greater vulnerability were less likely to participate. Results of web-based studies may not adequately generalize to the general population. Trial registration: The trial was registered at current controlled trials: ISRCTN55991918.

中文翻译：

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一项基于网络的预防不健康饮酒的简短随机试验：参与者自我选择与男性年轻成人来源人群的比较

背景 随机对照试验 (RCT) 样本在多大程度上代表或不同于其来源人群是一个具有挑战性的问题，对结果的普遍性具有重大影响。这对于在随机对照试验中测试的可免费获得的基于网络的干预措施尤其重要，因为它们旨在覆盖广泛的人群，如果它们无法覆盖到更脆弱的个体，则可能会增加健康差异。我们评估了基于网络的初级/二级预防简短干预随机对照试验参与者样本与其来源人群的代表性。然后，我们将招募的人与未招募的随机对照试验中的人进行了比较。方法 瑞士对 19 岁的男性有强制性的征兵程序。2010 年 8 月至 2011 年 7 月，12 日，564 名男性（来源人群）参加了两个招聘中心，并被要求回答有关酒精使用的筛查问卷。在完成它的 11,819 人（94.1%）中，7027 人（59.5%）同意参加一项定期评估的纵向队列研究。2012 年，这些参与者被邀请参加基于网络的简短干预 RCT。参与不依赖于酒精使用的存在或数量。我们评估了随机对照试验样本相对于源人群的代表性，并比较了随机对照试验中招募/未招募的参与者在教育水平和酒精使用方面的情况。结果 RCT 样本与源人群不同：20 岁及以上的个体的代表性显着降低（34.3% 对 37.9%，p = 0.006），教育水平较低的个体（58.6% 对 63.0%，p = 0.0009）也是如此。RCT 人群中任何酒精使用的流行率较高（92.3% 对 90.6%，p = 0.03），但不健康饮酒的比例较低（37.1% 对 43.2%，p < 0.0001）。当在 RCT 中招募的人与未招募的人进行比较时，类似地发现了酒精使用措施和教育的差异，包括在多变量模型中，显示出较少不健康的酒精使用与高等教育和 RCT 中的招募之间的独立关联。结论 RCT 参与者与来源人群的其他成员不同，参与 RCT 的参与者任何酒精使用的流行率较高，但消费水平较低，不健康饮酒指标的流行率较低。在 RCT 样本中，受过高等教育的个体比例过高。饮酒范围的两端都可能存在选择偏差，具有某些更大脆弱性指标的个人不太可能参与。基于网络的研究结果可能无法充分推广到普通人群。试验注册：该试验在当前对照试验中注册：ISRCTN55991918。