"Drug court evaluations have been widely criticized for methodological weaknesses and data inconsistencies. Some criticisms stem from the fact that the majority of drug court program evaluations (1) have either no comparison group or a biased comparison group, such as offenders who refused or failed the drug court program; (2) report outcomes only for participants who complete the program (graduates), while excluding participants who did not complete the program (dropouts); and (3) use flawed data-collection methods, such as drug court participants’ self-reported surveys.52"

Source

Franco, Celinda, "Drug Courts: Background, Effectiveness, and Policy Issues for Congress," Congressional Research Service (Washington, DC: Library of Congress, October 12, 2010), p. 13.
http://www.fas.org/sgp/crs/mi…