Adherence Measurement
This page categorizes adherence measurements into direct and indirect methods, explaining each modality. Use the drop-down menu to explore the advantages, disadvantages, and examples from nutrition studies. Click here to learn more about self-reported measure types.
Directly measured methods involve measuring through indicators or proxies that do not directly measure adherence.
Example measures: liquid chromatography-mass spectrometry
Description: The concentration of a drug, its byproducts, or tracer compounds are measured in a sample of the patient’s hair.
Advantages
Some drug treatments and tracer compounds can stay in hair for weeks or months, allowing researchers to measure long-term adherence through this modality. Taking hair samples from participants is also less invasive.
Disadvantages
Drugs and tracer compounds cannot usually be measured immediately after the participant ingests the drug, which limits this modality’s use in determining short-term adherence patterns. Individual participant factors such as drug metabolism rates and drug interactions other medications that the participant is taking can also impact the accuracy of measuring adherence through hair samples. Finally, the high costs and logistic complexities of obtaining and using the lab equipment and assays necessary to determine drug samples through this modality are often high barriers in lower-resource settings.
Example Studies
Read the abstract here.
Example measures: hemoglobin levels
Description: The concentration of a drug, its byproducts, or tracer compounds are measured in a sample of the patient’s blood.
Advantages
Drug treatments and tracer compounds appear in the blood quickly after ingestion, allowing researchers to measure short-term adherence through this modality. Adherence classifications may also exist for adherence measurements using this modality (e.g., cutoffs for adherence based on drug levels of an antiretroviral medication in a patient’s blood).
Disadvantages
Drugs and tracer compounds are broken down in the body over time, which limits this modality’s use in determining long-term adherence patterns. Individual participant factors such as drug metabolism rates and drug interactions other medications that the participant is taking can also impact the accuracy of measuring adherence through blood samples. Taking blood samples may also be painful or invasive for participants. Finally, the high costs and logistic complexities of obtaining and using the lab equipment and assays necessary to determine drug samples through this modality are often high barriers in lower-resource settings.
Example Studies
Read the abstract here.
Example measures: ELISA
Description: The concentration of a drug, its byproducts, or tracer compounds are measured in a sample of the patient’s urine.
Advantages
Drug treatments and tracer compounds can appear in urine quickly after ingestion, allowing researchers to measure short-term adherence through this modality. Taking urine samples from participants is also less invasive.
Disadvantages
Individual participant factors such as drug metabolism rates and drug interactions other medications that the participant is taking can also impact the accuracy of measuring adherence through urine samples. Finally, the high costs and logistic complexities of obtaining and using the lab equipment and assays necessary to determine drug samples through this modality are often high barriers in lower-resource settings.
Example Studies
Read the abstract here.
Example measures: digital pill system
Description: A capsule containing an integrated radio-frequency sensor encapsulates a drug to create a digital pill. This digital pill transmits information about the drug ingestion to a wearable device, which subsequently sends the data to a computer.
Advantages
Using an electronic device that directly measures adherence can provide real-time records of adherence to researchers that captures daily adherence patterns. These devices are also sometimes ingested with the medication, which does not add additional burden on participants to measure adherence.
Disadvantages
The high costs and technological infrastructure needed to measure adherence through this modality can create high barriers in lower-resource settings. Participants must have a smartphone and Bluetooth and Wi-Fi/cellular data to accurately measure adherence. Participants may also need to have good command of technology if the measure requires participants to download an app or send their results to researchers. If a technological error occurs, a technician may need to come help the researchers or participants, which may take time.
Example Studies
Read the abstract here.
Indirectly measured methods involve measuring the drug, its metabolites, or biological markers to assess adherence directly.
Example measures: Morisky Medication Adherence Scale-8, Simplified Medication Adherence Questionnaire, Adherence to Refills and Medicines Scale
Description: Patients respond to questions about their medication-taking behavior, barriers and facilitators to taking medications, etc.
Advantages
Self-reported questionnaires are often easy to administer, low cost, and not invasive to participants. They are also a quick way to collect data and require minimal resources. Validated questionnaires can be used, which may have existing adherence classifications that separate participants into adherence categories based on their responses.
Disadvantages
To create a good questionnaire, many rounds of pre-testing may be required, which can be time and resource intensive. Questionnaires also often monitor adherence retrospectively, and participants may struggle to recall past behaviors accurately. For questionnaires administered by an interviewer, their communication skills and phrasing of questions can affect participants’ responses. An interviewer’s presence can also increase the likelihood of social desirability bias if the participant provides responses that they think the interviewer wants to hear.
Example Studies
Read the article summary here.
Read the article summary here.
Example measures: in-clinic pill counts
Description: Staff at a health facility count the number of remaining pills over a defined amount of time.
Advantages
Pill counts are often a low cost, non-invasive, and easy way to measure adherence. They can be integrated into routine refill or healthcare visits easily. They are also a quick way to collect data and require minimal resources.
Disadvantages
Pill counts often do not capture adherence patterns (e.g., what days pills were missed, when in the day pills were taken, etc.). Social desirability bias may also occur if participants know the amount of pills they should have and are reporting their pill-taking behavior to a healthcare worker. Pill counts are often measured as the number of pills taken of a defined amount of time. If participants’ pills are counted earlier than this timeframe, adherence may be underestimated. If participants’ pills are counted later than this timeframe, adherence may be overestimated.
Example Studies
Read the article summary here.
Read the article summary here.
Example measures: Medication event monitoring system (MEMS)
Description: Typically, a cap that attaches to standard medicine bottles and records the time and date each time the bottle is opened and closed.
Advantages
Electronic devices can reliably measure medication openings for a long time (years). This modality is non-invasive and can capture daily adherence patterns in real-time. Often, the device can send data to researchers or healthcare workers with minimal participant burden.
Disadvantages
Participants may find the device annoying or bulky and remove it from their medication container. Each device can be expensive and take time to replace if it is lost, stolen, or broken. Technical support for the researchers and participants may also be needed to set up the devices and troubleshoot any issues. After data collection, the research team also needs to follow up with participants to retrieve the devices.
Example Studies
Read the abstract here.
Example measures: medical records, pharmacy records
Description: Records from health care workers or pharmacies about previous adherence behaviors including prescription refills or biological assay results.
Advantages
Administrative records are useful for retrospective studies. This modality is a low-cost way to gather adherence data for large populations. There is often no burden to patients.
Disadvantages
Depending on the number of times participants go to pharmacies or healthcare facilities, there may be few data points per participant. Administrative records often do not capture adherence patterns (e.g., what days pills were missed, when in the day pills were taken, etc.). This modality also often only measures the maximum possible adherence for pharmacy or refill records. Precisely measuring adherence or partial adherence can be difficult. Data about treatment or medications outside of the system are likely to be missed. In settings with weaker healthcare infrastructure, gathering and analyzing administrative records can be difficult to conduct.
Example Studies
Read the abstract here.