Health Education & Behavior 40(2) 206 –215 © 2012 Society for Public Health Education Reprints and permission:

Traditionally, randomization is used to evaluate prevention and treatment programs in order to increase internal validity and accuracy of conclusions about effectiveness (Leykin et al., 2007). However, randomization may affect who partici-pates in random control trials and thus may not reflect the larger population, which includes those who would not par-ticipate in a study because they want control over their treat-ment as well as those who would participate regardless of whether they have control over their treatment. Substantial theory and research suggest that better outcomes may occur when individuals are able to choose their own treatment, as having a choice is thought to act to motivate individuals (Patall, Cooper, & Robinson, 2008). Early research showed that people were more likely to engage in, and find more pleas-ant, activities they had chosen (Lewin, 1952; Zimbardo