We created a “supply diary” for each patient in the
cohort, indicating whether medication was available on
each day during the 360 days of follow-up. This diary
linked all observed statin fills based on the dispensing
date and the days’ supply. We calculated the proportion of
days covered (PDC) during each of 12 consecutive 30-day
periods of follow-up and created a binary indicator for
“full adherence” each month, defined as PDC ≥0.8 (or ≥24
days covered, equivalently). This PDC value corresponds
to the level of use above which patients with coronary
artery disease benefit from statins16 and the threshold employed
by most quality measures.