Table 1 Terminology and operational definitions of medication adherence used in hypertension literature

Continuous multiple –interval gap (CMG) [24–26]

• “Percentage of days that a patient did not possess medication” [24, 26]

• \( \frac{{\mathrm{Total}\ \mathrm{number}\ \mathrm{of}\ \mathrm{days}\ \mathrm{without}\ \mathrm{medications}\ \mathrm{between}\ \mathrm{first}\ \mathrm{and}\ \mathrm{last}\ \mathrm{fills}}^{\mathrm{a}}}{\mathrm{Number}\ \mathrm{of}\ \mathrm{days}\ \mathrm{between}\ \mathrm{first}\ \mathrm{and}\ \mathrm{last}\ \mathrm{pharmacy}\ \mathrm{fills}} \) [25]

• 1 year [24, 26]

• <20% or <0.20 [24, 25]

• Division into 3 groups [26]:

<20%, 20% to 59%, and ≥60%

Continuous single- interval medication availability (CSA) [25]

• \( \frac{\mathrm{Days}\ \mathrm{supply}\ \mathrm{a}\mathrm{t}\ \mathrm{a}\ \mathrm{single}\ \mathrm{pharmacy}\ \mathrm{fill}}{\mathrm{Number}\ \mathrm{of}\ \mathrm{days}\ \mathrm{before}\ \mathrm{t}\mathrm{he}\ \mathrm{next}\ \mathrm{pharmacy}\ \mathrm{fill}\ \mathrm{for}\ \mathrm{t}\mathrm{he}\ \mathrm{same}\ \mathrm{medication}} \) [25]

• 1 year [25]

• ≥0.80 [25]

Medication Possession Ratio (MPR) [13, 25, 27–33], or Medication Refill Adherence [34]

• \( \frac{\mathrm{Total}\ \mathrm{days}\ \mathrm{supply}\ \mathrm{from}\ {1}^{\mathrm{st}}\ \mathrm{fill}\ \mathrm{date}\ \mathrm{to}\ \mathrm{last}\ \mathrm{fill}\ {\mathrm{date}}^{\mathrm{a}}}{\mathrm{Days}\ \mathrm{between}\ \mathrm{first}\ \mathrm{fill}\ \mathrm{date}\ \mathrm{to}\ \mathrm{last}\ \mathrm{fill}\ \mathrm{date}} \) [25, 27, 29, 30, 34]

• 6 months [27, 33]

• No dichotomization- Presented as a quantitative measure [33]

• \( \frac{\mathrm{Total}\ \mathrm{days}\ \mathrm{supply}\ \mathrm{between}\ {1}^{\mathrm{st}}\ \mathrm{fill}\ \mathrm{date}\ \mathrm{to}\ \mathrm{last}\ \mathrm{fill}\ \mathrm{date}}{\mathrm{Days}\ \mathrm{in}\ \mathrm{the}\ \mathrm{study}\ \mathrm{period}} \) [28, 32]

• 9 months [34]

• ≥80% or ≥ 0.80 [13, 25, 27, 29, 30, 34, 35]

• \( \frac{\mathrm{Total}\ \mathrm{days}\ \mathrm{supply}\ \mathrm{between}\ {1}^{\mathrm{st}}\ \mathrm{fill}\ \mathrm{date}\ \mathrm{to}\ \mathrm{last}\ \mathrm{fill}\ \mathrm{date}}{\mathrm{Fixed}\ \mathrm{observation}\ \mathrm{period}\ \left(\mathrm{e}.\mathrm{g}.\ 1\ \mathrm{year}\right)} \) [35]

• 1 year [27, 31, 32, 35]

• Division into 3 groups [28, 32]:

80–100%: High adherence

50–79%: Moderate adherence

<50%: Low adherence

• \( \frac{\mathrm{Total}\ \mathrm{days}\ \mathrm{supply}\ \mathrm{between}\ {1}^{\mathrm{st}}\ \mathrm{fill}\ \mathrm{date}\ \mathrm{to}\ \mathrm{last}\ \mathrm{fill}\ \mathrm{date}\ }{\mathrm{Fixed}\ \mathrm{observation}\ \mathrm{period}\ \left(\mathrm{e}.\mathrm{g}.\ 1\ \mathrm{year}\right)\ } \) [31]

• 3 years [28]

• \( \frac{\mathrm{Number}\ \mathrm{of}\ \mathrm{days}\ \mathrm{with}\ \mathrm{medication}}{\mathrm{Days}\ \mathrm{in}\ \mathrm{study}\ \mathrm{period}} \) [13]

• Up to 4 years [13]

• \( \frac{\frac{\mathrm{Number}\ \mathrm{of}\ \mathrm{tablets}\ \mathrm{dispensed}}{\mathrm{Daily}\ \mathrm{dose}}\times \left(\mathrm{Number}\ \mathrm{of}\ \mathrm{dispensing}\mathrm{s}-1\right)}{\mathrm{Number}\ \mathrm{of}\ \mathrm{days}\ \mathrm{between}\ \mathrm{last}\ \mathrm{and}\ \mathrm{first}\ \mathrm{dispensing}} \) [33]

• Up to 6 years [30]

Proportion of Days Covered (PDC) [36, 37]

• “The proportion of days covered by any anti-hypertensive medication… determined based on number of days supplied and quantity of medication dispensed for each prescription” [37]

• 3 months [37]

• ≥0.80 [36, 37]

• \( \frac{\mathrm{Number}\ \mathrm{of}\ \mathrm{days}\ \mathrm{with}\ \mathrm{medication}}{\mathrm{Days}\ \mathrm{in}\ \mathrm{study}\ \mathrm{period}} \) [36]

• 1 year [36]

MedsIndex [33]

• “Score out of 100 calculated from prescription refill history” [33]

• \( \frac{\mathrm{Days}\ \mathrm{supply}\ \mathrm{a}\mathrm{t}\ \mathrm{a}\ \mathrm{single}\ \mathrm{pharmacy}\ \mathrm{fill}}{\mathrm{Number}\ \mathrm{of}\ \mathrm{a}\mathrm{ctual}\ \mathrm{days}\ \mathrm{between}\ \mathrm{repeats}} \) [38]

• 6 months [33]

• No dichotomization- Presented as a quantitative measure [33]