title: Design of the Trial of Activity in Adolescent Girls (TAAG).
abstract: The primary aim of the Trial of Activity in Adolescent Girls (TAAG) is to test an intervention to reduce by half the age-related decline in moderate to vigorous physical activity (MVPA) in middle school girls. The intervention will be evaluated using a group-randomized trial involving 36 middle schools. The primary endpoint is the mean difference in intensity-weighted minutes (i.e., MET-minutes) of MVPA between intervention and comparison schools assessed using accelerometry. The TAAG study design calls for two cross-sectional samples, one drawn from 6th graders at the beginning of the study and the second drawn from 8th graders at the end of the study following the 2-year implementation of the intervention. An important strength of this design over a cohort design is the consistency with the goals of TAAG, which focus on environmental-level rather than individual-level interventions to produce change. The study design specifies a recruitment rate of 80% and a smaller sample of girls at baseline (n=48 per school) than at follow-up (n=96 per school). A two-stage model will be used to test the primary hypothesis. In the first stage, MET-weighted minutes of MVPA will be regressed on school, time (baseline or follow-up), their interaction, ethnicity and week of data collection. The second stage analysis will be conducted on the 72 adjusted means from the first stage. In the main-effects model, we will regress the follow-up school mean MET-weighted minutes of MVPA on study condition, adjusting for the baseline school mean. The TAAG study addresses an important health behavior, and also advances the field of group-randomized trials through the use of a study design and analysis plan tailored to serve the main study hypothesis.
authors.affiliation: University of North Carolina at Chapel Hill, USA. June_Stevens@unc.edu
authors.forename: June
authors.initials: J
authors.lastname: Stevens
authors.forename: David M
authors.initials: DM
authors.lastname: Murray
authors.forename: Diane J
authors.initials: DJ
authors.lastname: Catellier
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Hannan
authors.forename: Leslie A
authors.initials: LA
authors.lastname: Lytle
authors.forename: John P
authors.initials: JP
authors.lastname: Elder
authors.forename: Deborah R
authors.initials: DR
authors.lastname: Young
authors.forename: Denise G
authors.initials: DG
authors.lastname: Simons-Morton
authors.forename: Larry S
authors.initials: LS
authors.lastname: Webber
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior; D000367:Age Factors; D002648:Child; D003430:Cross-Sectional Studies; D015444:Exercise; D005260:Female; D006293:Health Promotion; D006801:Humans; D008019:Life Style; D016032:Randomized Controlled Trials as Topic / Q000379:methods*; D012107:Research Design; D012574:Schools