Medication possession ratio: implications of using fixed and variable observation periods in assessing adherence with disease-modifying drugs in patients with multiple sclerosis

The purpose of this study was to compare two methods of adherence calculation using administrative data for patients with multiple sclerosis (MS) who are prescribed disease-modifying drugs.Pharmacy-billed disease-modifying drug prescription claims were selected from the 2007-2008 LifeLink™ Health Plan Claims Database. The index date was the first disease-modifying drug prescription claim. Two cohorts were created: all patients with a...