title: Group-based trajectory modeling to assess adherence to biologics among patients with psoriasis.
abstract: BACKGROUND
  Proportion of days covered (PDC), a commonly used adherence metric, does not provide information about the longitudinal course of adherence to treatment over time. Group-based trajectory model (GBTM) is an alternative method that overcomes this limitation.
  
  
  METHODS
  The statistical principles of GBTM and PDC were applied to assess adherence during a 12-month follow-up in psoriasis patients starting treatment with a biologic. The optimal GBTM model was determined on the basis of the balance between each model's Bayesian information criterion and the percentage of patients in the smallest group in each model. Variables potentially predictive of adherence were evaluated.
  
  
  RESULTS
  In all, 3,249 patients were included in the analysis. Four GBTM adherence groups were suggested by the optimal model, and patients were categorized as demonstrating continuously high adherence, high-then-low adherence, moderate-then-low adherence, or consistently moderate adherence during follow-up. For comparison, four PDC groups were constructed: PDC Group 4 (PDC ≥75%), PDC Group 3 (25%≤ PDC <50%), PDC Group 2 (PDC <25%), and PDC Group 1 (50%≤ PDC <75%). Our findings suggest that the majority of patients (97.9%) from PDC Group 2 demonstrated moderate-then-low adherence, whereas 96.4% of patients from PDC Group 4 showed continuously high adherence. The remaining PDC-based categorizations did not capture patients with uniform adherence behavior based on GBTM. In PDC Group 3, 25.3%, 17.2%, and 57.5% of patients exhibited GBTM-defined consistently moderate adherence, moderate-then-low adherence, or high-then-low adherence, respectively. In PDC Group 1, 70.8%, 23.6%, and 5.7% of patients had consistently moderate adherence, high-then-low adherence, and continuously high adherence, respectively. Additional analyses suggested GBTM-based categorization was best predicted by patient age, sex, certain comorbidities, and particular drug use.
  
  
  CONCLUSIONS
  GBTM is a more appropriate way to model dynamic behaviors and offers researchers an alternative to more traditional drug adherence measurements.
authors.affiliation: Novartis Pharmaceuticals Corporation, East Hanover, NJ, USA.
authors.forename: Yunfeng
authors.initials: Y
authors.lastname: Li
authors.affiliation: KMK Consulting Inc., Florham Park, NJ, USA.
authors.forename: Huanxue
authors.initials: H
authors.lastname: Zhou
authors.affiliation: Novartis Pharmaceuticals Corporation, East Hanover, NJ, USA.
authors.forename: Beilei
authors.initials: B
authors.lastname: Cai
authors.affiliation: Novartis Pharmaceuticals Corporation, East Hanover, NJ, USA.
authors.forename: Kristijan H
authors.initials: KH
authors.lastname: Kahler
authors.affiliation: Novartis Pharmaceuticals Corporation, East Hanover, NJ, USA.
authors.forename: Haijun
authors.initials: H
authors.lastname: Tian
authors.affiliation: Novartis Pharmaceuticals Corporation, East Hanover, NJ, USA.
authors.forename: Susan
authors.initials: S
authors.lastname: Gabriel
authors.affiliation: Novartis Pharmaceuticals Corporation, East Hanover, NJ, USA.
authors.forename: Steve
authors.initials: S
authors.lastname: Arcona
keywords: behavior; classification; dynamic; grouping; patterns; proportion days of covered (PDC)
references.citation: Med Care. 2005 Jun;43(6):521-30
references.pmid: 15908846
references.citation: J Clin Epidemiol. 1997 Jan;50(1):105-16
references.pmid: 9048695
references.citation: Arch Intern Med. 2007 Mar 26;167(6):540-50
references.pmid: 17389285
references.citation: Circulation. 2009 Jun 16;119(23):3028-35
references.pmid: 19528344
references.citation: J Eur Acad Dermatol Venereol. 2012 May;26 Suppl 3:61-7
references.pmid: 22512682
references.citation: Med Care. 1988 Aug;26(8):814-23
references.pmid: 3398608
references.citation: Annu Rev Clin Psychol. 2010;6:109-38
references.pmid: 20192788
references.citation: Value Health. 2007 Jan-Feb;10(1):3-12
references.pmid: 17261111
references.citation: Clin Ther. 2012 Jan;34(1):190-9
references.pmid: 22284998
references.citation: J Quant Criminol. 2010 Dec;26(4):445-453
references.pmid: 21132047
references.citation: J Dermatolog Treat. 2013 Feb;24(1):64-9
references.pmid: 21797808
references.citation: Ann Pharmacother. 2006 Jul-Aug;40(7-8):1280-88
references.pmid: 16868217
references.citation: Psychiatr Serv. 2007 Jun;58(6):864-7
references.pmid: 17535949
references.citation: Med Care. 2013 Sep;51(9):789-96
references.pmid: 23685406
references.citation: J Pediatr Psychol. 2010 Oct;35(9):1028-37
references.pmid: 20304772
references.citation: Med Care. 2002 Sep;40(9):794-811
references.pmid: 12218770
references.citation: J Drugs Dermatol. 2013 Oct;12(10):1090-2
references.pmid: 24085042
references.citation: Clin Ther. 1999 Jun;21(6):1074-90; discussion 1073
references.pmid: 10440628
references.citation: Qual Saf Health Care. 2004 Jun;13(3):172-5
references.pmid: 15175485