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Table 4 Linear mixed effects regression model evaluating the relationship between monthly copayment and medication adherence (n = 12389 )*

From: Effect of electronic prescribing with formulary decision support on medication tier, copayments, and adherence

Patient or Claim Characteristic Adherence, expressed as absolute percent change in proportion of days covered P value
Copayment in dollars 4 -8% <0.0001
Medication class – inhaled steroid -49% <0.0001
Zip code-based estimates of patients’ annual income  
$45 k – $75 k 6% <0.0001
> $75 k 8% <0.0001
Medication dosing frequency greater than once daily -4% <0.0001
  1. *Variables without association, and therefore not used as predictors in this model, are: patient age, gender, history of depression (as evidenced by prior use of antidepressants), and patient race (as estimated from zip code data).
  2. The referent categories were as follows: angiotensin receptor blocker medication class, annual income < $45 k annually, and medication dosing less than or equal to once daily.
  3. Estimated based on zip code data. 336 claims were excluded from this analysis due to missing zip code data.