Adherence to medical advice: measuring non-adherence

Psychology A2 · Health Psychology. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

Adherence can be measured in three ways. Subjective measures ask the patient or family, in a clinical or semi-structured interview or a questionnaire. They are cheap and can explain why doses are missed, but patients tend to overstate adherence. Riekert and Drotar (1999) studied adolescents with diabetes and their parents and found that families who did not complete the study measures had poorer adherence, so samples can be biased.

Objective measures record behaviour: pill counts and electronic dispensers that log each opening. Chung and Naya (2000) used an electronic cap with asthma patients and found high adherence, with pill counts giving a slightly higher figure.

Biological measures test blood or urine for the drug. They show the drug was taken, but are invasive and costly.

Rules to remember

Pill count adherence (%) = tablets taken ÷ tablets prescribed × 100.
Tablets taken = tablets given − tablets left.
Self-report: quick, gives reasons (qualitative data), but social desirability lowers validity.
Pill count: objective and cheap, but missing tablets may have been thrown away, not swallowed.
Electronic dispenser: records date and time of each opening; opening the cap does not prove the dose was swallowed.
Blood or urine test: direct evidence the drug is in the body; shows recent intake only.

Common mistake

In pill counts, students divide the tablets left by the tablets given. That gives the percentage missed; adherence uses the tablets taken.

Worked example

A patient is given 90 tablets to take over 30 days, three a day. After 30 days, 18 tablets remain. What is her adherence by pill count?

Tablets prescribed = 3 × 30 = 90.
Tablets taken = 90 − 18 = 72.
Adherence = 72 ÷ 90 × 100 = 80%.

Answer: 80%

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