The number of repeated observations needed to estimate the habitual physical activity of an individual to a given level of precision
The number of repeated observations needed to estimate the habitual physical activity of an individual to a given level of precision
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DOI：
10.1371/journal.pone.0192117
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发表时间：
2018-02-01
期刊：
影响因子：
3.7
通讯作者：
Bergman, Patrick
中科院分区：
文献类型：
--
作者：
Bergman, Patrick
身体活动行为每天，每周，甚至跨季节自然变化。为了评估一个人的身体活动的习惯水平，必须对这个人进行足够长的监测，以便在考虑到这种自然的人内变化的情况下可以识别该水平。一个重要的问题，一个其答案对研究和调查设计、流行病学研究和人口监测有影响的问题是，在这样的习惯水平或模式可以被识别到期望的精确度之前，个体需要被监测多久？本研究的目的是估计需要重复观察的次数，以确定一个人的习惯性体力活动行为的给定程度的精度。50名瑞典成年人连续四周佩戴加速度计。计算了在95%的时间内，个人日常体力活动在5-50%范围内所需的天数。为了了解估计值的不确定性，所有统计估计值都被引导了2000次。在95%置信度下，观察所需的平均测量天数在个体习惯性体力活动的20%以内，对于剧烈体力活动最高，需要182天。对于久坐行为，等效天数为2.4天。为了将80%的样本捕获到其习惯性体力活动水平的+/- 20%内，如果久坐行为是感兴趣的结果，则需要3.4天，MVPA需要34.8天。本研究表明，对于需要在个体水平上获得准确数据的分析，应使用比传统的7天方案更长的测量收集期。此外，MVPA的量与确定习惯性体力活动水平所需的天数呈负相关，表明最不活跃的人也是最难确定习惯性体力活动水平的人。这些结果可能对旨在分析个人数据的研究人员产生重要影响。在更新关于适当监测方案的建议之前，应在不同人群中重复本研究。
Physical activity behavior varies naturally from day to day, from week to week and even across seasons. In order to assess the habitual level of physical activity of a person, the person must be monitored for long enough so that the level can be identified, taking into account this natural within-person variation. An important question, and one whose answer has implications for study-and survey design, epidemiological research and population surveillance, is, for how long does an individual need to be monitored before such a habitual level or pattern can be identified to a desired level of precision? The aim of this study was to estimate the number of repeated observations needed to identify the habitual physical activity behaviour of an individual to a given degree of precision. A convenience sample of 50 Swedish adults wore accelerometers during four consecutive weeks. The number of days needed to come within 5-50% of an individual's usual physical activity 95% of the time was calculated. To get an idea of the uncertainty of the estimates all statistical estimates were bootstrapped 2000 times. The mean number of days of measurement needed for the observation to, with 95% confidence, be within 20% of the habitual physical activity of an individual is highest for vigorous physical activity, for which 182 days are needed. For sedentary behaviour the equivalent number of days is 2.4. To capture 80% of the sample to within +/- 20% of their habitual level of physical activity, 3.4 days is needed if sedentary behavior is the outcome of interest, and 34.8 days for MVPA. The present study shows that for analyses requiring accurate data at the individual level a longer measurement collection period than the traditional 7-day protocol should be used. In addition, the amount of MVPA was negatively associated with the number of days required to identify the habitual physical activity level indicating that the least active are also those whose habitual physical activity level is the most difficult to identify. These results could have important implications for researchers whose aim is to analyse data on an individual level. Before recommendations regarding an appropriate monitoring protocol are updated, the present study should be replicated in different populations.