Department of Biostatistics and Research Epidemiology, Henry Ford Health System, Detroit, MI, USA.
Trials. 2011 Jun 6;12:141. doi: 10.1186/1745-6215-12-141.
To assess bias and generalizability of results in randomized controlled trials (RCT), investigators compare participants to non-participants or early- to late-participants. Comparisons can also inform the recruitment approach, especially when working with challenging populations, such as urban adolescents. In this paper, we describe characteristics by participant status of urban teens eligible to participate in a RCT of a school-based, web-based asthma management program.
The denominator for this analysis was all students found to be eligible to participate in the RCT. Data were analyzed for participants and non-participants of the RCT, as well as for students that enrolled during the initially scheduled recruitment period (early-participants) and persons that delayed enrollment until the following fall when recruitment was re-opened to increase sample size (late-participants). Full Time Equivalents (FTEs) of staff associated with recruitment were estimated.
Of 1668 teens eligible for the RCT, 386 enrolled early, and 36 enrolled late, leaving 1246 non-participants. Participants were younger (p < 0.01), more likely to be diagnosed, use asthma medication, and have moderate-to-severe disease than non-participants, odds ratios (95% Confidence Intervals) = 2.1(1.7-2.8), 1.7(1.3-2.1), 1.4(1.0-1.8), respectively. ORs were elevated for the association of late-participation with Medicaid enrollment, 1.9(0.7-5.1) and extrinsic motivation to enroll, 1.7(0.6-5.0). Late-participation was inversely related to study compliance for teens and caregivers, ORs ranging from 0.1 to 0.3 (all p-values < 0.01). Early- and late-participants required 0.45 FTEs/100 and 3.3 FTEs/100, respectively.
Recruitment messages attracted youth with moderate-to-severe asthma, but extending enrollment was costly, resulting in potentially less motivated, and certainly less compliant, participants. Investigators must balance internal versus external validity in the decision to extend recruitment. Gains in sample size and external validity may be offset by the cost of additional staff time and the threat to internal validity caused by lower participant follow-up.
ClinicalTrials.gov: NCT00201058.
为了评估随机对照试验（RCT）中结果的偏倚和推广性，研究人员将参与者与非参与者或早期至晚期参与者进行比较。这些比较还可以为招募方法提供信息，特别是在与具有挑战性的人群（如城市青少年）合作时。在本文中，我们描述了有资格参加一项基于学校的、基于网络的哮喘管理计划 RCT 的城市青少年按参与者状态划分的特征。
这项分析的分母是所有被发现有资格参加 RCT 的学生。对 RCT 的参与者和非参与者、在最初预定的招募期内注册的学生（早期参与者）以及在招募重新开放以增加样本量时延迟注册到次年秋季的学生（晚期参与者）进行了数据分析。还估计了与招募相关的全职员工（FTE）。
在有资格参加 RCT 的 1668 名青少年中，有 386 名早期参与者，36 名晚期参与者，其余 1246 名是非参与者。参与者更年轻（p<0.01），更有可能被诊断、使用哮喘药物且疾病程度为中重度，比值比（95%置信区间）分别为 2.1（1.7-2.8）、1.7（1.3-2.1）和 1.4（1.0-1.8）。晚期参与者与医疗补助计划的参与、外在动机的关联呈上升趋势，分别为 1.9（0.7-5.1）和 1.7（0.6-5.0）。晚期参与者与青少年和护理人员的研究依从性呈反比，比值比范围从 0.1 到 0.3（所有 p 值<0.01）。早期和晚期参与者分别需要 0.45 FTE/100 和 3.3 FTE/100。
招募信息吸引了患有中重度哮喘的青少年，但延长招募时间成本高昂，导致参与者的动机和依从性降低。研究人员必须在延长招募的决定中平衡内部有效性与外部有效性。样本量的增加和外部有效性的提高可能会被额外的员工时间成本以及因参与者随访率降低而导致的内部有效性受到威胁所抵消。
ClinicalTrials.gov：NCT00201058。
