The effects of copayments on medication adherence during the first two years of prescription drug treatment
Journal of Occupational and Environmental Medicine
http://www.ncbi.nlm.nih.gov/pubmed/?term=The%20effects%20of%20copayments%20on%20medication%20adherence%20during%20the%20first%20two%20years%20of%20prescription%20drug%20treatment.