title: Why is greater medication adherence associated with better outcomes.
abstract: BACKGROUND
  Previous studies found an association of greater adherence to placebo medication with better outcomes. The present study tested whether this association was explained by any of the following factors: 1) adherence to other medications, 2) healthcare behaviors, 3) disease risk, or 4) predicted degree of adherence. Data included information on more than 800 risk factors from 27,347 subjects in two randomized controlled trials of hormone therapy in the Women's Health Initiative.
  
  
  RESULTS
  Greater adherence to placebo was not associated with colon cancer but was substantially and significantly associated with several diverse outcomes: death, myocardial infarction, stroke, and breast cancer. Adherence to hormone therapy was only weakly associated with outcomes. The WHI risk factors only poorly predicted degree of adherence, R2 < 4%. No underlying factors accounted for the association between placebo adherence and outcome.
  
  
  CONCLUSIONS
  The results suggest that adherence to placebo is a marker for important risk factors that were not measured by WHI. Once identified these risk factors may be used to increase the validity of observational studies of medical treatment by reducing unmeasured confounding.
authors: Health Services Research, Huntsman Cancer Institute, University of Utah School of Medicine, Salt Lake City, UT 84112, USA. hartzarthur@gmail.com.
authors: Arthur
authors: A
authors: Hartz
authors: Tao
authors: T
authors: He
references: Ann Epidemiol. 2003 Oct;13(9 Suppl):S122-8
references: 14575944
references: J Affect Disord. 2006 Feb;90(2-3):217-21
references: 16360216
references: Control Clin Trials. 1998 Feb;19(1):61-109
references: 9492970
references: Lancet. 1990 Sep 1;336(8714):542-5
references: 1975045
references: J Bone Miner Res. 2011 Apr;26(4):683-8
references: 20939064
references: Med Care. 2011 May;49(5):427-35
references: 21422960
references: BMJ. 2006 Jul 1;333(7557):15
references: 16790458
references: Arch Intern Med. 2007 Apr 23;167(8):847-52
references: 17452550
references: Circulation. 2009 Apr 21;119(15):2051-7
references: 19349320
references: Epidemiology. 1990 Jan;1(1):43-6
references: 2081237
references: Lancet. 2005 Dec 10;366(9502):2005-11
references: 16338449
references: Ann Epidemiol. 1996 Mar;6(2):93-101
references: 8775589
references: BMJ. 2009 Jun 16;338:b2137
references: 19531550
references: Osteoporos Int. 2011 Mar;22(3):943-54
references: 20532481
references: N Engl J Med. 1980 Oct 30;303(18):1038-41
references: 6999345
references: J Gen Intern Med. 2011 May;26(5):546-50
references: 21203857
references: Ann Epidemiol. 2003 Oct;13(9 Suppl):S5-17
references: 14575938
references: J Bone Miner Res. 2011 Apr;26(4):681-2
references: 21433070
references: Med Care. 2009 Mar;47(3):334-41
references: 19194337