Univariate dynamic screening system: An approach for identifying individuals with irregular longitudinal behavior

In our daily lives, we often need to identify individuals whose longitudinal behavior is different from the behavior of those well-functioning individuals, so that some unpleasant consequences can be avoided. In many such applications, observations of a given individual are obtained sequentially, and it is desirable to have a screening system to give a signal of irregular behavior as soon as possible after that individuals longitudinal behavior starts to deviate from the regular behavior, so that some adjustments or interventions can be made in a timely manner. This article proposes a dynamic screening system for that purpose in cases when the longitudinal behavior is univariate, using statistical process control and longitudinal data analysis techniques. Several different cases, including those with regularly spaced observation times, irregularly spaced observation times, and correlated observations, are discussed. Our proposed method is demonstrated using a real-data example about the SHARe Framingham Heart Study of the National Heart, Lung and Blood Institute. This article has supplementary materials online.