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Potential bias in medication adherence studies of prevalent users.

Publication ,  Journal Article
Maciejewski, ML; Bryson, CL; Wang, V; Perkins, M; Liu, C-F
Published in: Health Serv Res
August 2013

PURPOSE: We examined how the choice of historic medication use criteria for identifying prevalent users may bias estimated adherence changes associated with a medication copayment increase. METHODS: From pharmacy claims data in a retrospective cohort study, we identified 6,383 prevalent users of oral diabetes medications from four VA Medical Centers. Patients were included in this prevalent cohort if they had one fill both 3 months prior and 4-12 months prior to the index date, defined as the month in which medication copayments increased. To determine whether these historic medication use criteria introduced bias in the estimated response to a $5 medication copayment increase, we compared adherence trends from cohorts defined from different medication use criteria and from different index dates of copayment change. In an attempt to validate the prior observation of an upward trend in adherence prior to the date of the policy change, we replicated time series analyses varying the index dates prior to and following the date of the policy change, hypothesizing that the trend line associated with the policy change would differ from the trend lines that were not. RESULTS: Medication adherence trends differed when different medication use criteria were applied. Contrary to our expectations, similar adherence trends were observed when the same medication use criteria were applied at index dates when no copayment changes occurred. CONCLUSION: To avoid introducing bias due to study design in outcomes assessments of medication policy changes, historic medication use inclusion criteria must be chosen carefully when constructing cohorts of prevalent users. Furthermore, while pharmacy data have enormous potential for population research and monitoring, there may be inherent logical flaws that limit cohort identification solely through administrative pharmacy records.

Duke Scholars

Published In

Health Serv Res

DOI

EISSN

1475-6773

Publication Date

August 2013

Volume

48

Issue

4

Start / End Page

1468 / 1486

Location

United States

Related Subject Headings

  • Time Factors
  • Prescription Drugs
  • Middle Aged
  • Medication Adherence
  • Male
  • Humans
  • Health Services Research
  • Health Policy & Services
  • Female
  • Drug Costs
 

Citation

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ICMJE
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Maciejewski, M. L., Bryson, C. L., Wang, V., Perkins, M., & Liu, C.-F. (2013). Potential bias in medication adherence studies of prevalent users. Health Serv Res, 48(4), 1468–1486. https://doi.org/10.1111/1475-6773.12043
Maciejewski, Matthew L., Chris L. Bryson, Virginia Wang, Mark Perkins, and Chuan-Fen Liu. “Potential bias in medication adherence studies of prevalent users.Health Serv Res 48, no. 4 (August 2013): 1468–86. https://doi.org/10.1111/1475-6773.12043.
Maciejewski ML, Bryson CL, Wang V, Perkins M, Liu C-F. Potential bias in medication adherence studies of prevalent users. Health Serv Res. 2013 Aug;48(4):1468–86.
Maciejewski, Matthew L., et al. “Potential bias in medication adherence studies of prevalent users.Health Serv Res, vol. 48, no. 4, Aug. 2013, pp. 1468–86. Pubmed, doi:10.1111/1475-6773.12043.
Maciejewski ML, Bryson CL, Wang V, Perkins M, Liu C-F. Potential bias in medication adherence studies of prevalent users. Health Serv Res. 2013 Aug;48(4):1468–1486.
Journal cover image

Published In

Health Serv Res

DOI

EISSN

1475-6773

Publication Date

August 2013

Volume

48

Issue

4

Start / End Page

1468 / 1486

Location

United States

Related Subject Headings

  • Time Factors
  • Prescription Drugs
  • Middle Aged
  • Medication Adherence
  • Male
  • Humans
  • Health Services Research
  • Health Policy & Services
  • Female
  • Drug Costs