Modelling a response as a function of high-frequency count data: The association between physical activity and fat mass
Modelling a response as a function of high-frequency count data: The association between physical activity and fat mass
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DOI：
10.1177/0962280215595832
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发表时间：
2017-10-01
影响因子：
2.3
通讯作者：
Ness, Andy R.
中科院分区：
文献类型：
--
作者：
Augustin, Nicole H.;Mattocks, Calum;Ness, Andy R.
加速度计广泛应用于健康科学、生态学和其他应用领域。它们将身体活动的强度量化为给定时间段内每个时期的计数。目前，健康科学家使用加速度计时间序列的非常有损的摘要，其中一些是基于活动水平的粗略离散化，并做出某些隐含的假设，包括身体活动的线性或恒定影响。我们提出的直方图作为一个功能性的总结，实现一个近乎无损的降维，个人的时间序列之间的可比性和易于解释。使用直方图作为功能摘要避免了加速度计计数在时间上的配准。在我们的新方法中，标量响应回归加性多维函数预测，包括高频计数的直方图，和其他连续协变量的加性非线性预测。该方法改进了当前最先进的技术，因为它可以处理不同长度和缺失值的高频时间序列，并以更少的假设产生一种灵活的方式来模拟身体活动的影响。它还允许测试通常的建模假设。我们调查的反应脂肪量和身体活动之间的关系，通过加速度计测量，在雅芳纵向研究的父母和孩子的数据。我们的方法可以测试身体活动的影响是否因性别、一天中的时间或一周中的天数而异。我们表明，有意义的解释需要仔细处理的可识别性约束的总和到一个属性的直方图。我们发现，（不一定是因果关系）的影响，体力活动对公斤脂肪质量不是线性的，也不是恒定的活动强度。
Accelerometers are widely used in health sciences, ecology and other application areas. They quantify the intensity of physical activity as counts per epoch over a given period of time. Currently, health scientists use very lossy summaries of the accelerometer time series, some of which are based on coarse discretisation of activity levels, and make certain implicit assumptions, including linear or constant effects of physical activity. We propose the histogram as a functional summary for achieving a near lossless dimension reduction, comparability between individual time series and easy interpretability. Using the histogram as a functional summary avoids registration of accelerometer counts in time. In our novel method, a scalar response is regressed on additive multi-dimensional functional predictors, including the histogram of the high-frequency counts, and additive non-linear predictors for other continuous covariates. The method improves on the current state-of-the art, as it can deal with high-frequency time series of different lengths and missing values and yields a flexible way to model the physical activity effect with fewer assumptions. It also allows the commonly made modelling assumptions to be tested. We investigate the relationship between the response fat mass and physical activity measured by accelerometer, in data from the Avon Longitudinal Study of Parents and Children. Our method allows testing of whether the effect of physical activity varies over its intensity by gender, by time of day or by day of the week. We show that meaningful interpretation requires careful treatment of identifiability constraints in the light of the sum-to-one property of a histogram. We find that the (not necessarily causal) effect of physical activity on kg fat mass is not linear and not constant over the activity intensity.