Assessing intervention effects in a school-based nutrition intervention trial: which analytic model is most powerful?

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.

Predictors of smoking intentions and smoking status among nonsmoking and smoking adolescents.

Purpose: To examine predictors of smoking intentions among current adolescent nonsmokers and smokers as well as risk factors associated with smoking status.

Methods: Adolescents (N=237), ages 12 through 18 years, were asked to complete a questionnaire that assessed smoking behavior and variables thought to be related to smoking. Cognitive-motivational variables including perceived vulnerability and optimism, not previously examined in adolescent smoking studies, were also included.

School-based approaches to affect adolescents' diets: results from the TEENS study.

This article reports on the outcomes of the Teens Eating for Energy and Nutrition at School (TEENS) study, a 2-year intervention study conducted in 16 middle schools with a goal of increasing students' intakes of fruits, vegetables, and lower fat foods. Despite positive interim results for students randomized to intervention schools, the positive effects of the intervention were not seen for the primary outcomes at the end of the 2nd year. Positive effects were seen only for a food choice score (suggesting that the students usually choose lower versus higher fat foods) and not for measures of food intake.

Assessing the most powerful analysis method for school-based intervention studies with alcohol, tobacco, and other drug outcomes.

This article compares four mixed-model analyses valid for group-randomized trials (GRTs) involving a nested cohort design with a single pretest and a single posttest, the most common design used in GRTs. This study makes estimates of intraclass correlations (ICCs) available to investigators planning GRTs with alcohol, tobacco, and other drug measures as the outcomes of interest. It also provides formulae demonstrating the potential benefits to the standard error of the intervention effect of both adjustments for fixed and time-varying covariates, as well as correlations over time.

Design and analysis of group-randomized trials: a review of recent methodological developments.

We review recent developments in the design and analysis of group-randomized trials (GRTs). Regarding design, we summarize developments in estimates of intraclass correlation, power analysis, matched designs, designs involving one group per condition, and designs in which individuals are randomized to receive treatments in groups. Regarding analysis, we summarize developments in marginal and conditional models, the sandwich estimator, model-based estimators, binary data, survival analysis, randomization tests, survey methods, latent variable methods and nonlinear mixed models, time series methods, global tests for multiple endpoints, mediation effects, missing data, trial reporting, and software.

Design and analysis of group-randomized trials: a review of recent practices.

We reviewed group-randomized trials (GRTs) published in the American Journal of Public Health and Preventive Medicine from 1998 through 2002 and estimated the proportion of GRTs that employ appropriate methods for design and analysis. Of 60 articles, 9 (15.0%) reported evidence of using appropriate methods for sample size estimation.

Predicting adolescents' intake of fruits and vegetables.

Objective: To explore potential predictors of adolescents' fruit and vegetable intake by expanding on current theory and drawing from other adolescent research.

Design: This research reports on baseline and interim data from a school-based intervention study. Data were collected through surveys administered to students at the beginning and end of their 7th grade year.