Authors

• R. J. Cook
• J. F. Lawless

Abstract

Interest in the presence and nature of trend arises frequently in science, public health, technology, and many other areas. In this ar- ticle we discuss the notion of trend in the context of recurrent event processes. We discuss different frameworks within which one can inves- tigate trend and consider various ways in which trends may be manifest. Tests for trend are discussed in detail and the utility of intensity-based models is emphasized for characterizing event processes and understand- ing trends. Simulation studies are conducted to study the effect of het- erogeneity in the investigation of trend. Data from a study of hospi- talization patterns in patients with affective disorder are analysed for illustration.

Keywords

• Keywords. Intensity function
• recurrent events
• robust methods
• stochas- tic modeling
• Trend