Analysis of temporal survival trends: considerations and best practice

Monitoring quality of healthcare is vital to ensure that changes made to clinical practice achieve the intended goals. Assessing temporal trends due to the accumulated effect of all changes in clinical practice in a given period is essential in quality monitoring. However, this assesment is compplicated by the fact that numerous of changes might occour over time unrelated to the clinical practice. Furthermore, the methods used to assess temporal trends in patient outcomes in the medical literature are heterogeneous, making it difficult to compare results between studies. In this paper, we describe methods that enable researchers to investigate temporal trends in survival data and we discuss their pros and cons. Numerous unrelated changes may occur over time which must be taken into account and disentangled when assessing the improvement in clinical management. The methods and interpretation thereof are exemplified on patients with diffuse large B-cell lymphoma from the Danish lymphoma registry.