Compare ways to measure non-adherence
Compare interviews, pill counts, medication dispensers and biological measures, using Riekert and Drotar and Chung and Naya to evaluate validity and reliability.
Original StudyForA teaching mapped to Cambridge 9990 Health Psychology sections 3.2.1–3.2.3, 2028–2030 Version 1. Example and key studies are not official Cambridge materials or mark schemes. These lessons explain research; they do not advise anyone to start, stop or change treatment.
Before you begin
- This lesson covers Cambridge Psychology 9990 Health Psychology section 3.2.2. Measures are research tools; the lesson is not a request to collect anyone's medical data.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which statement best compares a pill count and an electronic medication cap?
What you will learn
- Subjective clinical and semi-structured interviews; Riekert and Drotar (1999)
- Objective pill counts and medication dispensers; Chung and Naya (2000)
- Biological measures using blood and urine samples
Choose a measure that matches the behaviour
A subjective measure asks a person or clinician to describe treatment behaviour. A clinical or semi-structured interview can ask about routines, understanding, reasons, missed doses and context. Open questions may reveal details a fixed response misses; structured prompts make answers easier to compare. Self-report can be affected by memory, social desirability, question wording and willingness to disclose.
The Cambridge syllabus places Riekert and Drotar (1999) in its section on subjective clinical and semi-structured interviews. Their study examined participation in research on adherence among adolescents with insulin-dependent diabetes and also reports study questionnaires and adherence scores. Ninety-four families were grouped as non-consenters, non-returners and participants. Non-returners had lower adherence scores and the adolescents tested blood sugar less often than participants; participants and non-consenters did not differ on the available data.
The study demonstrates a selection problem: people who return study materials may differ in adherence from those who do not. Its evidence warns that a sample of respondents can overstate adherence or be less representative. It does not show that every interview or self-report is inaccurate, and the abstracted group comparisons do not establish why families did not return materials.
Counts and dispensers record different traces
A pill count compares the number of tablets issued with the number returned or remaining. A medication dispenser or electronic cap can record when a compartment or bottle is opened. These measures can make behaviour more observable and produce counts or timing patterns, but an opened container does not prove that the medicine was swallowed at that time.
Chung and Naya (2000) began a 12-week pilot of oral asthma medication with 57 participants; 47 completed it. An electronic TrackCap recorded each bottle-cap removal and replacement. Using TrackCap events, the median measure of tablet-count compliance was 89%, while the median measure of days with two openings at least eight hours apart was 71%. Returned-tablet counts gave a slightly higher median compliance estimate of 92%.
The two measures answer different questions: approximate quantity versus regularity of the prescribed schedule. TrackCap can reveal timing that a final pill count misses, but it records cap events, not ingestion. The pilot involved one medication and condition, had ten non-completers, and should not be generalised to all treatments or treated as a clinical recommendation.
Biological measures can indicate exposure at a point in time
A blood or urine sample can be analysed for a medicine, a metabolite or another biological marker. This is an objective laboratory reading and may provide evidence that exposure occurred within a relevant time window. It is not a complete record of every scheduled dose or the person's reasons for taking or not taking treatment.
Interpretation depends on the medicine, the time since a dose, metabolism, sample handling, the assay and the relevant comparison range. A recent dose may be detected even if earlier doses were missed; a substance may be absent for reasons other than intentional non-adherence. Sampling can also be costly, intrusive or impractical, so consent and appropriate clinical oversight matter.
No single measure captures every aspect of adherence. Interviews can explain why; counts and dispensers can describe quantities or patterns; biological samples can indicate exposure at a specific time. Combining suitable measures may strengthen an account, but disagreement between them is evidence to investigate rather than a reason to assume one measure is always correct.
Sources for this lesson
- Cambridge International AS & A Level Psychology 9990 syllabus, 2028–2030
- Cambridge International AS & A Level Psychology 9990 Reference List, 2028–2030
- Riekert and Drotar (1999), Who participates in research on adherence to treatment in insulin-dependent diabetes mellitus?
- Chung and Naya (2000), Compliance with an oral asthma medication: a pilot study using an electronic monitoring device
Pause and explain
Why did Riekert and Drotar's results matter for interpreting adherence research?
Worked example
A clinic's pill count suggests that nearly all tablets were removed, but an electronic cap shows irregular openings. Explain why the results need not contradict each other.
Show the worked solution
- State what each measure records: remaining tablets versus opening times.
- Explain that the count estimates quantity while the cap can show a pattern across time.
- Note that neither measure proves ingestion; check definitions, collection period and context before interpreting.
Answer The pill count estimates how many tablets are missing from the supply, whereas the electronic cap records when the bottle was opened. Someone could remove several tablets at once, and an opening is not proof of swallowing. The measures answer different questions, so the result calls for careful interpretation and possibly a respectful interview rather than an accusation.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A study reports a 92% median pill-count estimate and a 71% median schedule-adherence estimate from an electronic cap. Interpret the difference.
Give me a hint
First identify the numerator or event each measure uses.
Compare my reasoning
- Pill-return counts estimate how many tablets are missing from the dispensed supply.
- The electronic-cap schedule measure counts days with two recorded openings at least eight hours apart.
- A person may remove tablets without following the schedule; neither trace alone proves ingestion.
The 92% estimate is a median count-based measure of quantity, while the 71% estimate is a median count of days meeting the recorded timing rule. They are not interchangeable. The TrackCap recorded openings rather than swallowing, so the gap suggests that quantity and schedule regularity can differ.
Look for these in your work
- Both definitions stated
- Quantity and timing distinguished
- Ingestion limitation included
Researchers interview only families who return questionnaires. Use Riekert and Drotar to evaluate the risk in this sampling decision.
Give me a hint
Compare respondents and non-returners without assuming every family has the same pattern.
Compare my reasoning
- In the study, non-returners had lower adherence scores and adolescents tested blood sugar less often than participants.
- A sample made only of returners may over-represent families with higher measured adherence or greater organisation.
- This is a non-response concern for the sampled context; it does not prove the reason each family failed to return materials or describe every population.
Riekert and Drotar found lower measured adherence among non-returners than participants, so analysing only returned materials risks a systematically different sample. The study supports reporting recruitment and non-response and using follow-up where appropriate. It does not prove why every family did not respond or that all studies have the same bias.
Look for these in your work
- Relevant group result used
- Sampling risk explained
- Generalisation bounded
Plan a study that compares a self-report measure with an objective trace over a defined period, while respecting privacy.
Give me a hint
Define the behaviour and period, obtain consent, and keep measures separate.
Compare my reasoning
- State the treatment behaviour and observation period, then ask participants to complete a brief, non-leading self-report about that same period.
- With consent and appropriate oversight, compare it with a suitable count or dispenser record; explain what that trace does and does not record.
- Use secure, minimised data, report participation and missing data, and analyse agreement without calling either measure a perfect gold standard.
A valid comparison uses the same clearly defined period and behaviour for both measures. The objective trace must match the treatment and record its limits; the self-report should allow honest answers without blame. Consent, privacy and non-response reporting are essential. Agreement can strengthen confidence, while disagreement needs investigation rather than automatic dismissal of one source.
Look for these in your work
- Behaviour and time window defined
- Measures and limits distinguished
- Consent and privacy included
Common mistakes
- Calling self-report useless instead of evaluating its strengths and limitations
- Assuming a returned questionnaire represents every invited family
- Treating a pill count or cap opening as proof that a dose was swallowed
- Comparing a quantity measure with a timing measure as if they were identical
- Treating one blood or urine sample as a complete record over time
- Ignoring attrition, measurement definitions and the sample's context
What can you explain now?
What did Chung and Naya's TrackCap record, and why is it not proof that each dose was swallowed?
Compare with the explanation
It recorded the date and time the medication bottle cap was removed and replaced; an opening does not establish that a tablet was taken or swallowed.
An objective trace can improve the record without measuring every part of the behaviour of interest.
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Make it stick
Compare one subjective, one objective and one biological measure of non-adherence, including what each records and one limitation.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.