Methods to Assess Medication Adherence
The descriptions of data collection methods are presented in Table 4.
Out of 33 studies used data collection methods to measure medication
adherence, 22 (66.6%) studies used a self-report data collection
method, pharmacy refill and claims database 9 (27.3%), and pill count 2
(6.1%). Moreover, the selected studies used various data sources; the
majority obtained from patients (n=21), and direct methods were not used
in the included studies. As previously mentioned the variation of the
prevalence of medication adherence, the rate of adherence as assessed by
using self-reported, claims database/refill data, pill count, health
provider’s report (self-report, patient record) ranged from 10.6% to
81%, 19,21-23,34,46-62 10% to
62.9%,25,34,63-70 45%,71,72 and
69.2% to 85.4%,34,58 respectively. The most common
included studies utilized standardized and structured data collection
tool, and structured interviews to measure adherence. Morisky Medication
Adherence Scale-8 items (MMAS) and the four-item Morisky Green Levine
Medication Adherence Scale (MGLS) self-report measure was the most
common measures used for evaluating medication adherence, which was
applied in 5 (23.8%),22,23,46,47,51 and 4 (19%)
studies,52,53,55,56 respectively.
Nine studies used the electronic data records (pharmacy or medical
claims database) to measure medication adherence, which different
measures were utilized, including the percentage of days covered (PDC),
medicine possession ratio (MPR), prescription fill, and missing days.
The PDC is the number of days a patient gets each medication divided by
the number of days for eligibility for medication, greater than 80%
mean patient have adequate adherence, which 80 % considered cut-off
between adherent and nonadherent patients as used by LeBlanc et
al.68 Also, the MPR is the number of days that doses
were dispersed divided by the total number of days between the first and
last doses. It is dichotomized into greater than 80% considered
adherent and lower than or equal 80% considered nonadherent as used by
Holvast et al66, and Slabbert et
al69 reported that patients considered adherence if
MPR was between ≥80% and ≤110%.
Regarding prescription fill and missing days, nonadherence described if
medication discontinued before 180 days after the index refill
date.63 Other studies defined adherence as the
proportion of compliance during the first 24 weeks from prescription
fill.67 Also, Yau et al25 measured
adherence as filled prescriptions for medications with no gaps of more
than 15 days within six months after the start of treatment. On the
other hand, two studies used pill count by calculating the actual number
of pills taken dividing by the expected number of pills taken during the
study period and multiplying by 100.71 Other study was
calculated by the total number of weeks the participants took
medication.72