Title: Research Designs for Complex Community Interventions for Childhood Obesity Prevention
1Research Designs for Complex Community
Interventions for Childhood Obesity Prevention
- Robert W. Jeffery, Ph.D.
- Division of Epidemiology
- University of Minnesota
- School of Public
- May 4-5, 2004
2Hypothesis
Changes in the food environment of middle schools
and high schools will reduce the prevalence of
overweight in students.
3Design Option 2-Group Randomized Trial
- Unit of randomization is school
- Primary outcome, change in BMI, is measured on
students. - Two-year duration
4School Selection Eligibility Criteria
- Co-educational
- Student ages 12-18
- At least 2-year attendance expectation
- Feasibility of intervention
- Feasibility of data collection
- Consent of school
- Satisfactory consent procedure for students
5Recruitment Enrollment Procedure
- Random selection of schools to approach
- Possible stratification by public/private, SES,
ethnic composition (stratification very limited) - Age range (e.g., middle school, high school)
6Intervention Components Food Service
- School lunch
- A la carte
- Vending machines
7Food Service Targets
- Reduce overall availability of food at school
- Increase availability of low-energy food
- Decrease availability of high-energy food
- Increase price of high-energy food
- Decrease price of low-energy food
- Reduce food advertising on campus
8Primary Outcome
- Change in BMI measured at baseline, 12 months,
and 24 months - Measured in as many students as possible who
attend school for the 2-year period
9Secondary Measures
- Individual level (self-report)
- Diet
- Physical activity
- Demographics
- Psychosocial measures
- Intervention exposure
- School level (direct observation)
- Intervention implementation
- Food sales
10Pretest-Posttest Control Group Design
R O X O OR 0 0 0
11Threats to Validity Internal
- Differential experience not related to treatment
as a function of treatment group - Measurement or dropout bias by treatment group
(lack of blinding is problematic, but unavoidable)
12Threats to Validity External
- Volunteer bias, both individual and school
- Limited school pool
- Feasibility constraints
- Overall sample size
13Pragmatic IssuesCost
- Maintaining good fidelity of intervention
delivery can be costly, since school food
service, a la carte food service, and vending
involve different business operations. - Objective assessment of food sales can also be
costly. - Number of schools is a major determinant of cost.
14Pragmatic IssuesQuality Control
- Political considerations often make intervention
implementation incomplete. - Food service is a dynamic activity that requires
careful monitoring. - Large sample size may reduce quality of
intervention.
15Analysis IssuesSources of Variance in Outcomes
- Individual characteristics
- Intervention variability
- School effect
16Analysis OptionsBy School
- Maximum protection against threats to internal
and external validity - Including individual characteristics and
intervention fidelity terms reduces variance - Cost of producing enough replications to achieve
adequate power is problematic
17Analysis OptionsBy Individual
- Internal validity threatened by differential
factors between schools other than
interventionplausibility of this threat is
estimable by historical data - Individual level and intervention delivery
effects may again be useful covariates - External validity and generalizability are weak
with this approach
18Summary Conclusion
- The group randomized trial is the gold standard
for evaluating community intervention trials. - It is strong on both internal and external
validity and thus provides a strong evidential
basis for important decisions like public health
policy. - It is not necessary for establishing the
plausibility of an intervention approach. - Thus, it is best thought of as representing the
culmination of a line of research in an area
rather than a prerequisite for research funding
related to community intervention.