Which method of adherence measurement is most suitable for daily use to predict virological failure among immigrant and non-immigrant HIV-1 infected patients?

In industrialized countries, virological failure occurs more often among HIV-infected immigrant patients. Non-adherence is the most credible explanation. We compared adherence of immigrant patients with that of non-immigrant patients in the Netherlands, and investigated which method of adherence measurement is most suitable for daily use to predict virological treatment failure: testing knowledge of the current regimen, a quantitative adherence interview, pharmacy prescription refill ratio (dispensed medication divided by prescribed medication, DM/PM), and plasma drug levels.