Retention Issues in Urban School-Based Randomized Trials

Objective: This study examines the retention rate among two cohorts of kindergarten children who completed their exit examination in 2nd grade as part of an ongoing randomized clinical trial (RCT) in an urban school district. Methods: A total of 562 kindergarten children from five elementary schools were recruited in three cohorts; Cohort I (207-2008), Cohort II (2008-2009), and Cohort III (2009-2010). Each cohort is followed until the middle of 2nd grade to test the effectiveness of xylitol vs. placebo gummy bears. Children also receive dental exams, oral health education, fluoride varnish, and sealant application in schools. To date, cohort I and cohort II completed the exit examination and cohort III will be followed until the end of December 2011. Bivariate analysis was used to compare socio-demographic, dental insurance status, decayed or filled teeth (dft) between children who were retained at exit exams versus those lost to follow-up. Results: Out of 374 children from cohorts I and II, 321 (86%) were retained at the end of Kindergarten, 232 (62%) at the end of 1st grade, and 189 (51%) children at the exit examination in 2nd grade. Out of 185 children who were not able to be followed, 181 were transferred out of school district and 4 dropped out for the project. Although children who were lost to follow up had higher proportion of males, African-Americans, single parent, Medicaid coverage, and decayed or filled teeth, they were not statistically significant. Conclusion: In this inner-city urban school district, there were progressive losses to follow-up over a two and a half year period. This study confirms the retention challenges that are to be expected when conducting urban school-based clinical trials in low-income and minority communities. Future investigators should take into account retention rates in sample size calculation. Supported by HRSA/MCHB R40-MC07838 and CTSC UL1RR024989.