The study design may also pose barriers. Participation in research, specifically behavioral interventions, often requires a time commitment that many participants are unwilling or unable to give. Participants often face time and financial constraints owing to competing demands of needing to work (even sometimes multiple jobs), or being the primary caretaker of children and/or relatives, or being the single head of a household (Adeyemi, Evans, & Bahk, 2009; Herring, Montgomery, Yancey, Williams, & Fraser, 2004; Wyatt et al., 2003). Logistical issues such as the need to travel to the research site, lack of transportation, or reservations about the neighborhood of the site may also prevent interest in participation. Randomization presents a particular challenge to recruitment because participants may prefer to make a choice rather than to be assigned to the available group options, fearing they may end up in a group contrary to their preference such as a control group (Broome & Richards, 2003; also see Chapter 8 on control group selection). In addition, excessive restrictions on eligibility may limit the ability to generate an adequate sample size needed for statistical power and representation of the target population (Yancey, Ortega, & Kumanyika, 2006).