太空舱 发表于 2016-8-3 14:06 
请问是2年数据不太可靠还是什么原因?谢谢!
there are two reasons increment's size cannot describe the process of change. First, it cannot tell us about the shape of each person's trajectory;Second, it cannot distinguish true change from measurement error. So, in statistical terms, two-waves studies cannot describe individual trajectories of change and they cannot confound true change with measurement error.