Assessing Intervention Effects in a School-Based Nutrition Intervention Trial: Which Analytic Model Is Most Powerful?

Abstract

This article compares four mixed-model analyses valid for group-randomized trials (GRTs) involving a nested cohort design with a single pretest and posttest. This study makes estimates of intraclass correlations (ICCs) available to investigators planning GRTs addressing dietary outcomes. It also provides formulae demonstrating the potential benefits to the standard error of the intervention effect (sigma(delta)) from adjustments for both fixed and time-varying covariates and correlations over time. These estimates will allow other researchers using these variables to plan their studies by estimating a priori detectable differences and sample size requirements for any of the four analytic options. These methods are demonstrated using data from the Teens Eating for Energy and Nutrition at School study. Mixed-model analyses of covariance proved to be the most powerful analysis in that data set. The formulae may be applied to any dependent variable in any GRT given corresponding information for those variables on the parameters that define the formulae.

Multilevel factorial experiments for developing behavioral interventions: Power, sample size, and resource considerations.

“…Janega et al (2004), Murray (1998), and Murray and Blitstein (2003) further discuss the use and relative merits of these models in a cluster-randomized experiment.…”

Relationships between executive cognitive function and lifetime substance use and obesity-related behaviors in fourth grade youth

“…Already low physical activity rates continue to decrease throughout childhood and into adolescence (Trost et al, 2002), and only about one third of all youth meet the recommended levels of fruit, grain, meat, dairy, and vegetable intake, whereas fat and sugars combine for 50% of energy intake (Muñoz, Krebs-Smith, Ballard-Barbash, & Cleveland, 1997). These statistics are particularly concerning since the lack of physical exercise, sedentary behavior, and poor eating behaviors among youth have all been identified as the primary risk factors for rapidly increasing obesity rates (Janega et al, 2004;McPherson, Hoelscher, Alexander, Scanlon, & Serdula, 2000).…”

Parent–child dietary intake resemblance in the United States: Evidence from a large representative survey

“…Most previous studies are based on small and local samples, and the possible regional and between-group differences in the resemblance between child and parental dietary intakes could affect our understanding of the relationships at the national level. It is crucial to assess such an interrelationship to guide future dietary intervention programs which to date have been strictly targeted towards schools among other non-household settings (Abdel Gawwad, Fetohy, Fiala, Al Orf, & Al Saif, 2006; Agozzino, Esposito, Genovese, Manzi, & Russo Krauss, 2007; Fahlman, Dake, McCaughtry, & Martin, 2008; Janega et al, 2004; Nicklas et al, 1997; Podrabsky, Streichert, Levinger, & Johnson, 2007). Although previous studies assessed nutrient and food group associations between family members, none have evaluated associations in overall diet quality.…”