Concept Architecture
Concept
Theoretically, Medication Possession Ratio (MPR) is a quantitative measure of medication adherence that estimates the proportion of time during a defined observation period for which a patient has medication available. It is based on pharmacy dispensing records rather than direct observation of medication-taking behaviour and serves as a proxy measure of adherence in pharmacoepidemiology, health services research and health economics. The concept exists to provide a standardised measure of medication availability that can be related to clinical outcomes, healthcare utilisation and costs.
Mathematically, Medication Possession Ratio is expressed as the ratio of the total number of days' supply of medication dispensed during an observation period to the total number of days in that period. The resulting ratio is commonly reported as either a proportion or percentage. Depending on study design, adjustments may be made for early refills, overlapping prescriptions or hospitalisations. Although MPR is closely related to the Proportion of Days Covered (PDC), it differs in that MPR may exceed 100% if excess medication is dispensed.
In practice, MPR is calculated using pharmacy claims or dispensing databases by summing the days' supply of all eligible prescriptions within a predefined observation period. It is widely used to evaluate adherence to treatments for chronic diseases, assess intervention effectiveness, estimate treatment persistence and examine the economic consequences of poor adherence. In health economic evaluations, MPR is frequently incorporated into analyses of healthcare utilisation, costs and treatment effectiveness.
Purpose
Used to quantify medication adherence from dispensing records, evaluate treatment utilisation, compare adherence across populations and assess the relationship between adherence, clinical outcomes and healthcare costs.
Mathematical Formulae
Primary Formula
MPR = (Total days' supply of medication dispensed � Number of days in the observation period) ? 100%
Supporting Formulae
As a proportion:
MPR = Total days' supply � Observation period
Adherence indicator:
Adherent = 1 if MPR � 0.80, otherwise 0
Related Mathematical Methods
- Proportion of Days Covered (PDC)
- Adherence Rate
- Persistence Analysis
- Survival Analysis
- Pharmacy Claims Analysis
Example
A patient receives three prescriptions during a 180-day observation period, each providing a 60-day supply.
Total days' supply = 60 + 60 + 60 = 180 days
MPR = (180 � 180) ? 100% = 100%
The patient demonstrates complete medication availability throughout the observation period according to the MPR measure.
Excel Implementation
| Function | Example Formula | Health Economics Application |
|---|---|---|
| SUM | =SUM(C2:C7) | Calculates the total days' supply dispensed. |
| DATEDIF | =DATEDIF(StartDate,EndDate,"d")+1 | Calculates the observation period in days. |
| IF | =IF(MPR>=0.8,"Adherent","Non-adherent") | Classifies patients using a predefined adherence threshold. |
| COUNTIFS | =COUNTIFS(MPRRange,">=0.8") | Counts adherent patients within a study cohort. |
| AVERAGE | =AVERAGE(MPRRange) | Calculates mean medication adherence across a population. |
VBA (Optional)
VBA can automate calculation of Medication Possession Ratio for large pharmacy claims databases and generate adherence reports across multiple patient cohorts.
Sources
- ISPOR Medication Compliance and Persistence Special Interest Group. Medication Compliance and Persistence: Terminology and Definitions.
- Steiner JF, Prochazka AV. The assessment of refill compliance using pharmacy records. Journal of Clinical Epidemiology. 1997.
- Andrade SE, Kahler KH, Frech F, Chan KA. Methods for evaluation of medication adherence and persistence using automated databases. Pharmacoepidemiology and Drug Safety. 2006.
- Drummond MF, Sculpher MJ, Claxton K, Stoddart GL, Torrance GW. Methods for the Economic Evaluation of Health Care Programmes.
- ISPOR Good Practice Reports.
Related Concepts (2)
Library
Publications
1
Pharmaceutical Care Practice: The Patient-Centered Approach to Medication Management — Cipolle, Strand & Morley, 3rd Edition ed., 2012 (McGraw-Hill)
The standard practical textbook for delivering pharmaceutical care and medication management services, setting out the philosophy of practice, the patient care process (assessment, care plan, follow-up), and drug-therapy problem identification.
BookView source →
Frequently Asked Questions (6)
What is the medication possession ratio?
A quantitative adherence measure calculated as the proportion of days within a period a patient had the medication available, based on refill data.
Source: Cramer et al. 2008
What proportion of days with medication does the medication possession ratio measure?
The medication possession ratio is a quantitative adherence measure based on prescription refills. It is calculated as the proportion of days within a period that a patient had the medication available. It is based on refill data, inferring possession from when the patient collected their prescriptions. It is a quantitative measure, a numerical ratio rather than a subjective judgement. It is closely related to proportion of days covered, another refill-based adherence measure that handles overlapping supply more precisely. The share of days a patient had the drug on hand is what it measures. Cramer and colleagues (2008) set this out.
Source: Cramer et al. 2008
How is the medication possession ratio calculated?
The medication possession ratio is calculated as the proportion of days within a period a patient had the medication available, so it is a quantitative adherence measure computed from that proportion, based on refill data. This calculation as the proportion of days with medication available defines it. So the medication possession ratio is a quantitative adherence measure calculated as the proportion of days within a period a patient had the medication available, based on refill data Being drawn from refill records, the measure is convenient and widely used, though having a supply on hand is not proof a patient actually took the doses.
Source: Cramer et al. 2008
On what data is the medication possession ratio based?
The medication possession ratio is based on refill data, so as a quantitative adherence measure it uses refill data to work out the proportion of days within a period a patient had the medication available. This basis in refill data defines it. So the medication possession ratio is a quantitative adherence measure calculated as the proportion of days within a period a patient had the medication available, based on refill data Being drawn from refill records, the measure is convenient and widely used, though having a supply on hand is not proof a patient actually took the doses.
Source: Cramer et al. 2008
What kind of measure is the medication possession ratio?
The medication possession ratio is a quantitative adherence measure, so it is a numerical adherence measure calculated as the proportion of days within a period a patient had the medication available, based on refill data. This character as a quantitative adherence measure defines it. So the medication possession ratio is a quantitative adherence measure calculated as the proportion of days within a period a patient had the medication available, based on refill data Being drawn from refill records, the measure is convenient and widely used, though having a supply on hand is not proof a patient actually took the doses.
Source: Cramer et al. 2008
How does the medication possession ratio relate to proportion of days covered?
The medication possession ratio relates to proportion of days covered as two refill-based adherence measures, the latter more precise on overlap: the medication possession ratio is the proportion of days within a period a patient had the medication available, and proportion of days covered is the proportion of days a patient had access to medication, accounting for overlapping supply more precisely than the medication possession ratio. So both use refill data, connected in that proportion of days covered handles overlapping supply more precisely Being drawn from refill records, the measure is convenient and widely used, though having a supply on hand is not proof a patient actually took the doses.
Source: Cramer et al. 2008
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