Ward et al. BMC Public Health 2011, 11:431 http://www.biomedcentral.com/1471-2458/11/431 Page 3 of 9 Figure 1 Conceptual model. The conceptual model for the Parenting SOS program is based on Darling and Steinberg’s Integrative Model of Parenting Ryan and Deci’s Self-Determination Theory, and incorporates parent goals and values, parenting style and stress, and parenting practices, which could influence child diet and activity behaviors as well as child weight. Participants and Recruitment Families with preschool-age children are being recruited in three waves using a variety of community resources including child care centers, direct mailings, community bulletin boards, listservs, and newspaper community announcements. The recruitment plan incorporates strategies to engage families from diverse racial, ethnic and socioeconomic backgrounds. For example, recruit- ment efforts are focused on counties located in central North Carolina with a large percentage of minority resi- dents. Additionally, child care centers that accept subsi- dies are specifically targeted to engage low-income families. Interested families are screened by phone. Eligibility criteria include having at least one child between the ages of 2 and 5 years old, at least one parent with a body mass index (BMI) greater than 25 (based on self- reported height and weight), willingness to participate in measures and intervention activities, and ability to speak English or comprehend standard age-level materials. Signed consent is then obtained from all participants when they arrive for baseline data collection. Parents sign consent for their own participation and that of their child. Power Calculation The study is powered on its primary outcome: mean change difference in child percent body fat, estimated from the Dezenberg et al. [17] formula between inter- vention and control children. The power calculation assumed an absolute change difference in percent body fat of 2% at the 35-week post-intervention point. The power calculation determined that 280 families needed to be recruited and randomized to provide at least 80% power, assuming a two-sided test at the 5% level, and a retention rate of 80% at the post-intervention assessment. Randomization For each wave, participants are first stratified by income (household income more or less than $50,000) and county. Household income of $50,000 represents the approximate median household income for the counties targeted for recruitment and was therefore selected as the cut point for income stratification. For each wave and county combination, two randomization tables (one for each income level) are created using SAS 9.2 (SAS Institute, Cary NC) with a randomization allocation ratio of 1:1 and a block size of 2 to ensure balance