Kaiser Permanente Washington Health Research Institute, Seattle, Washington.
Department of Epidemiology, University of Washington, Seattle, Washington.
Cancer Epidemiol Biomarkers Prev. 2020 Aug;29(8):1549-1556. doi: 10.1158/1055-9965.EPI-20-0388. Epub 2020 May 28.
Proportion of time covered (PTC, or "covered time") is a longitudinal measure of adherence to preventive health services, the use of which has increased in recent years. This measure is helpful for evaluating the success of delivering screening interventions over time. However, there are challenges and nuances in computing and interpreting PTC.
In this manuscript, we describe some desired properties of PTC measures, challenges in achieving those, and potential solutions using hypothetical examples.
We propose a modified PTC measure (mPTC) to complement the standard, existing PTC measure. The mPTC measure focuses on screening completion rather than initiation when a screening modality requires more than one step; is affected less by loss to follow-up, death, or cancer during covered time than the standard PTC measure; and is not sensitive to screening episode results. We propose weighting strategies to ensure that the average PTC and mPTC are more heavily influenced by individuals who were observed for longer and are thus more informative. We further describe how PTC and mPTC measures can incorporate test indication to focus specifically on screening.
We recommend that studies of covered time present ample descriptive information, calculate both PTC and mPTC, describe how symptoms and indication are handled, and present multiple complementary measures, such as the proportion never screened and the proportion in need of screening.
Common approaches, terminology, and reporting practices for covered time measures have the potential to improve the study of longitudinal cancer screening adherence.
时间覆盖率（PTC，或“覆盖时间”）是衡量预防保健服务依从性的纵向指标，近年来其应用有所增加。该指标有助于评估随时间推移提供筛查干预的效果。然而，计算和解释 PTC 存在挑战和细微差别。
在本文中，我们描述了 PTC 指标的一些理想属性、实现这些属性的挑战以及使用假设示例的潜在解决方案。
我们提出了一种改良的 PTC 指标（mPTC）来补充标准的现有 PTC 指标。mPTC 指标在筛查模式需要多个步骤时，更侧重于筛查完成而不是启动；在覆盖时间内，受随访丢失、死亡或癌症影响小于标准 PTC 指标；并且不受筛查期结果的影响。我们提出了加权策略，以确保平均 PTC 和 mPTC 受观察时间更长的个体的影响更大，从而更具信息量。我们进一步描述了 PTC 和 mPTC 指标如何纳入测试指标，以专门关注筛查。
我们建议对覆盖时间的研究提供充足的描述性信息，计算 PTC 和 mPTC，描述症状和指标的处理方式，并呈现多种互补指标，如从未接受过筛查的比例和需要筛查的比例。
覆盖时间指标的常见方法、术语和报告实践有可能改善对纵向癌症筛查依从性的研究。
