Background Internet-based cognitive-behavioural therapy (iCBT) is effective for subthreshold depression. However, which skills provided in iCBT packages are more effective than others is unclear. Such knowledge can inform construction of more effective and efficient iCBT programmes. Objective To examine the efficacy of five components of iCBT for subthreshold depression. Methods We conducted an factorial trial using a smartphone app, randomly allocating presence or absence of five iCBT skills including self-monitoring, behavioural activation (BA), cognitive restructuring (CR), assertiveness training (AT) and problem-solving. Participants were university students with subthreshold depression. The primary outcome was the change on the Patient Health Questionnaire-9 (PHQ-9) from baseline to week 8. Secondary outcomes included changes in CBT skills. Findings We randomised a total of 1093 participants. In all groups, participants had a significant PHQ-9 reduction from baseline to week 8. Depression reduction was not significantly different between presence or absence of any component, with corresponding standardised mean differences (negative values indicate specific efficacy in favour of the component) ranging between −0.04 (95% CI −0.16 to 0.08) for BA and 0.06 (95% CI −0.06 to 0.18) for AT. Specific CBT skill improvements were noted for CR and AT but not for the others. Conclusions There was significant reduction in depression for all participants regardless of the presence and absence of the examined iCBT components. Clinical implication We cannot yet make evidence-based recommendations for specific iCBT components. We suggest that future iCBT optimisation research should scrutinise the amount and structure of components to examine. Trial registration number UMINCTR-000031307. Data are available on reasonable request. After the publication of the primary findings, the deidentified and completely anonymised individual participant-level dataset will be posted on the UMIN-ICDR website () for access by qualified researchers.

中文翻译：

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1093 名大学生智能手机认知行为疗法治疗阈下抑郁症的组成部分：一项析因试验

背景 基于互联网的认知行为疗法 (iCBT) 对亚阈值抑郁症有效。然而，iCBT 包中提供的哪些技能比其他技能更有效尚不清楚。这些知识可以为构建更有效和高效的 iCBT 项目提供信息。目的 检验 iCBT 的五个组成部分对阈下抑郁症的疗效。方法 我们使用智能手机应用程序进行了析因试验，随机分配五种 iCBT 技能的存在与否，包括自我监控、行为激活 (BA)、认知重构 (CR)、自信训练 (AT) 和解决问题。参与者是患有亚阈值抑郁症的大学生。主要结果是患者健康问卷 9 (PHQ-9) 从基线到第 8 周的变化。次要结果包括 CBT 技能的变化。结果 我们随机分配了总共 1093 名参与者。在所有组中，参与者的 PHQ-9 从基线到第 8 周都有显着减少。抑郁症的减少在任何成分的存在或不存在之间没有显着差异，具有相应的标准化平均差异（负值表示有利于该成分的特定功效）范围BA 介于 -0.04（95% CI -0.16 至 0.08）之间，AT 介于 0.06（95% CI -0.06 至 0.18）之间。CR 和 AT 注意到特定的 CBT 技能改进，但其他的则没有。结论 无论是否存在所检查的 iCBT 组件，所有参与者的抑郁症都会显着减少。临床意义我们还不能针对特定的 iCBT 组件提出基于证据的建议。我们建议未来的 iCBT 优化研究应该仔细检查要检查的组件的数量和结构。试用注册号 UMINCTR-000031307。可应合理要求提供数据。主要研究结果公布后，去身份化和完全匿名的个人参与者级数据集将发布在 UMIN-ICDR 网站上（) 供合格的研究人员访问。