Table 1. Summary of Methods of Measuring Adherence.

Test	Example	Strength	Weakness
Direct method
Measurement of the level of metabolite in blood or urine	Measurement of serum 6-TGN level; infliximab and vedolizumab trough levels	- Objective - Useful in case of primary nonresponse and secondary loss of response to biological agents	- White coat adherence - Costly - Labor-intensive
Indirect method
Pill count	-	- Simple - Objective - Inexpensive	- Could associate with overestimation or underestimation of adherence - Not suitable for medications administered in nondiscrete dosages or taken on an as-needed basis
Pharmacy refill	Medication possession ratio, proportion of days covered method	- Objective - Relatively easy to obtain data	- Not equivalent to consumption of medication - Requires a closed pharmacy system
Electronic monitoring device	Medication Event Monitoring System	- Accurate - Results are easily quantified	- Expensive system - Requires return visits of patients
Patient self-report (e.g., patient-kept diaries, patient interviews, self-report questionnaires)	MMAS-4, MMAS-8, VAS, MARS-4	- Simple - Inexpensive	- Results could be easily manipulated by patients

TGN, thioguanine nucleotides; MMAS, Morisky Medication Adherence Scale; VAS, Visual Analogue Scale; MARS, Medication Adherence Reporting Scale.