Words can be cheap—and inaccurate—when it comes to tracking anti-HIV drug-taking. In a recent three-month study, Dr. Kathleen Melbourne of the University of Rhode Island asked 44 HIVers to report how many drug doses they missed. Self-report of adherence was consistently higher than that measured electronically by the Medication Event Monitoring Systems (MEMS) track cap. Participants’ pill bottles came equipped with MEMS, which has a computer chip that records the hour and date each time it is popped open.

The truth hurt: 24 percent of PWAs overestimated by 10 percent how many doses they took, and missed meds were documented in 98 percent of participants. Only one person took 100 percent of his meds in the three months. Use of the electro cap also revealed a wide degree of fluctuation in daily dosing times—another reason, Melbourne said, for drug failure.

“Self-reporting is the easiest way [to measure adherence], but it’s not reliable,” said Melbourne. “Patients won’t necessarily remember all the doses they missed.” However, with a $12,000 price tag to electronically monitor participants for 90 days, MEMS is a gold standard.