“…Several studies have emphasized the large variability of long‐term course among PD‐patients and linked heterogeneity to PD‐type/cluster and severity (Durbin & Klein, ; Hallquist & Lenzenweger, ; Kvarstein & Karterud, ; Seivewright, Tyrer, & Johnson, ; Tyrer, Tyrer, Yang, & Guo, ). Age‐related variability has also been observed in large longitudinal studies of PD (Johnson et al ., ) and in a naturalistic study of group psychotherapy (Lorentzen, Bogwald, & Hoglend, ).…”