SITAR growth curve analysis - a statistical method to assess longitudinal growth and development data

个别儿童的生长模式，如他们连续测量(例如，体重或身高)与年龄的关系曲线所代表的，可能是关于他们较早年龄的情况的信息，或者相反，它可能预测他们在以后的生活中患上疾病的风险，例如心脏病、中风或2型糖尿病。为了研究这一点，用一种简单的方式总结每个人的成长曲线的形状是有用的，这样它的形状就可以与他们之前或后来的经历联系在一起。生长曲线分析的SITAR方法就是最近开发的一种方法，它将每条个体的生长曲线概括为三个数字，分别反映它们的大小(即与其他人相比，它们是高还是矮，或者是重还是轻)，它们的生长节奏(即它们是相对成熟还是延迟生长的时间，例如女孩到达月经初潮的时候)，以及速度(它们与其他人相比生长的速度，例如青春期)。例如，一个个体可能相对较高，青春期较早，生长相对较快。此外，SITAR估计了一条平滑的平均增长曲线，可以与每个人的增长模式进行比较。令人惊讶的是，这个模型解释了几乎所有个体之间的增长差异，因此他们的大小、节奏和速度可以被视为对他们增长模式的完整总结。换句话说，当调整大小、节奏和速度时，它们的所有增长曲线看起来都是一样的(SITAR首字母缩写的意思是通过平移和旋转来叠加)。然后，很容易将个体的体型、节奏和速度的值与他们之前或后来的经历联系起来，并寻找与他们的增长模式之间的联系。

The pattern of growth in individual children, as represented by their growth curve of successive measurements (e.g. weight or height) plotted against age, may be informative about their circumstances at earlier ages, or conversely it may predict their risk of disease later in life, for example heart disease, stroke or type 2 diabetes. To investigate this it is useful to summarise the shape of each individual's growth curve in a simple way, so that its shape can be related to their earlier or later experiences. The SITAR method of growth curve analysis is a recently developed approach that does just this - it summarises each individual growth curve as just three numbers, reflecting respectively their size (i.e. whether they are tall or short, or heavy or light, as compared to others), their growth tempo (i.e. whether they are relatively mature or delayed in their timing of growth, e.g. when girls reach menarche), and velocity (how fast they are growing compared to others, e.g. in puberty). So for example an individual might be relatively tall, with early puberty, and growing relatively fast. In addition SITAR estimates a smooth average growth curve against which each individual's growth pattern can be compared. The surprising thing is that this model explains nearly all of the variability in growth between individuals, so that their size, tempo and velocity can be viewed as a complete summary of their growth pattern. Put another way, when adjusted for size, tempo and velocity all their growth curves look the same (the SITAR acronym mean Super-Imposition by Translation And Rotation). It is then simple to relate the values of size, tempo and velocity in individuals to their earlier or later experiences, and to look for links with their growth pattern.