PWM: School-based Programs to Prevent Overweight (2006)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
  • To create, implement and test a school based multiple risk factor reduction program for tenth grade high school students
  • To examine the effectiveness of the curriculum in increasing students’ knowledge of cardiovascular disease (CVD) risk factor concepts, decreasing CVD risk factor behaviors such as smoking, consumption of calories and foods high in saturated fat, cholesterol and salt, increasing levels of aerobic physical activity and consumption of complex carbohydrates and lowering heart rate, blood pressure, BMI and skinfold thickness
  • To provide adolescents with incentives for adopting a heart healthy lifestyle, cognitive and behavioral skills enabling them to make changes, additional specific skills for resisting influences and specific practice in using skills in order to strengthen perceived competence in employing newly acquired behaviors effectively.
Inclusion Criteria:

All tenth graders enrolled in four northern California high schools.

Exclusion Criteria:

None specified.

Description of Study Protocol:
  • Four senior high schools from two school districts participated in study; within each district, one school assigned at random to receive special intervention while other school served as control. Within districts, schools matched for size and ethnic distribution before randomization.
  • All tenth graders in each school scheduled to attend intervention sessions three days per week for seven weeks
  • Education program consisted of 20 classroom sessions, each lasting 50 minutes, occurring during regularly schedules physical education class time. First session introduced concept of healthy lifestyle; personal change notebooks with handouts, worksheets, homework assignments distributed to all students. Next 12 sessions divided into informational modules of physical activity, nutrition, cigarette smoking and stress; emphasis on immediate consequences, self-regulatory skills, discussion-oriented information sessions, performance-based exercises. Modules followed by a two-session competitive game, with students in teams competing for gift certificates. Final module of five sessions devoted to training in problem solving and development of action plan for behavior change.
  • Classroom instructors recruited from recent college graduates with experience in health related fields; teaching staff spent three days per week in the classroom, one day per week at Stanford preparing for activities
  • Assessments performed by trained staff over two days in each of four schools. Boys and girls separated into classrooms, completed self-administered questionnaires and physical measures in groups of 40 to 50 during each class period. Measurements collected at baseline and two months after completion of intervention. Regular school personnel did not participate in data collection.

Statistical Analysis

  • One way ANOVA and chi square tests to examine equivalence of treatment and control conditions at baseline
  • Two way ANCOVA and chi square tests to examine program effects.
Data Collection Summary:

Dependent Variables

  • Knowledge of CVD risk concepts: Measured by multiple choice tests covering physical activity, nutrition/diet and cigarette smoking
  • Physical activity: Self-reported by checklist featuring 19 forms of activity, five designated as activities that would provide aerobic training effect if performed for at least 20 minutes nonstop
  • Nutrition/diet: Self-reported by checklist presenting choices among 32 food pairs, one food in each pair superior with respect to diet/CVD relationships
  • Cigarette smoking: Self-reported frequency of use according to six frequency levels ranging from never to every day
  • Alcohol and marijuana use: Self-reported frequency checked by expired carbon monoxide measurements
  • Height, weight: Standard balance beam scale
  • BMI: Computed from height and weight
  • Subcutaneous skinfold thickness: Harpenden calipers –triceps and subscapular
  • Resting heart rate and blood pressure: After sitting quietly for three minutes, mean of three measurements used.

Independent Variables

Treatment (participation in intervention) vs. no treatment (no special intervention program introduced)

Control Variables

  • Sex
  • Race
  • Parents education.
Description of Actual Data Sample:
  • Original sample: 1,447 students responding to baseline survey (70% 15 years of age, 14% 14 years, 14% 16 years)
  • Withdrawals/Drop-outs: 317 failed to attend follow-up
  • Final sample: 1,130 students available at follow-up (treatment N=622, control N=508) (78%)
  • Location: Northern California
  • Race/Ethnicity: 69.0% White, 2.0% Black, 13.1% Asian, 6.4% Latino, 0.3% American Indian, 0.4% Pacific Islander, 8.9% other
  • SES: 50% of students fathers had completed four or more years of college.
Summary of Results:
  • At baseline, no significant differences in ethnic distribution, sex distribution, college enrollment plans, mean scores on combined knowledge test, reported cigarette or alcohol consumption, food choice score
  • Parents of students in control group had more education than parents of treatment group
  • Boys in treatment and control groups similar in anthropometric measurements, girls in control group had less body fat, lower heart rates, lower blood pressures than girls in treatment group. Higher proportion of girls in control group reported regular aerobic physical activity.
  • No differences found between drop-outs on knowledge or self-reported variables; treatment dropouts had mean triceps skinfold thickness of 14.7mm, control dropouts had mean thickness of 17.2mm (P=0.02)
  • Knowledge gains significantly greater for students in the treatment group on each of risk factor domains tested: Nutrition/diet, physical activity, cigarette smoking. In treatment group, boys increased combined score average of 11.1 points, girls average of 14.2 points.
  • Students classified as non-regular exercisers at baseline were principal target of intervention – higher proportion of those in the treatment group became regular exercisers at follow-up (treatment 30.2%, control 20%)
  • At follow-up, students in treatment group more likely to report that they would choose heart healthy snack items (increase in selection of 2.1 and 2.3 for boys and girls)
  • No significant differences between treatment and control groups in proportion of never smokers becoming smokers, proportion of regular smokers reporting cessation; more treatment students who were experimental smokers reported quitting at follow-up; 5.6% baseline experimental smokers in treatment group became regular smokers, 10.3% in control group
  • Strongest effects with resting heart rate: Boys and girls in treatment group reduced resting heart rate on average of 2.3 and 4.1 beats per minute; boys and girls in control group increased resting heart rate average of 0.4 beats per minute
  • Beneficial treatment effects observed for BMI: Treatment boys increased from 21.6 to 21.7kg per m2, treatment girls decreased from 22.1 to 21.9kg per m2; control boys increased from 20.9 to 21.3kg per m2, control girls remained at 21.4kg per m2 [main effect F (1, 1,060) = 3.7, P=0.05]
  • Beneficial effects also observed for triceps skinfold thickness [main effect F (1, 1,059) = 8.4, P=0.004] and subscapular skinfold thickness [main effect F (1, 1,058) = 6.4, P=0.01]
  • No treatment effect observed for systolic blood pressure; changes in diastolic blood pressure favored controls.
Author Conclusion:
  • One of first controlled trials of school based CVD risk factor reduction program for high school adolescents
  • Knowledge gains were pronounced, with students in treatment group increasing knowledge of risk factor concepts an average of 50%
  • Significantly greater proportion of students in treatment group initially classified as nonregular exercisers reported regular physical activity at follow-up
  • Impact of program on cigarette smoking also encouraging; quit rate among experimental smokers in treatment group significantly greater than quit rate in control group
  • Students self reports suggest significant changes were made in several CVD risk related behaviors
  • Reductions in body fat were achieved although the impact of the program appeared more consistent for girls. Reductions in all measures of body fat were observed among girls in the treatment condition while control group girls increased in skinfold thickness measures. Boys in both groups reduced on skinfold thickness measures but increases in BMI were greater for boys in control group.
  • Relationship between self reported behavior change and related physical measures is worth emphasizing
  • Limitation of study is that follow-up was conducted two months after a seven-week intervention; may not be sufficient amount of time to observe long term effects
  • Another limitation is that small number of schools may have undermined randomization; however, efforts were made to control for potential confounding variables (similar schools chosen, randomized within districts)
  • Finding that treatment and control drop-outs were similar on most baseline measures adds to authors confidence that internal validity of research was maintained
  • While school districts contained few Black students, other minorities accounted for almost 30%; study schools reflect fairly broad range with respect to ethnicity and SES. Other data also suggest comparability of sample to the general population.
  • Results strongly suggest that it is possible to increase adolescents’ understanding of CVD risk factor concepts, to modify number of relevant risk factor behaviors and to effect changes in certain physiologic parameters.
Funding Source:
Government: NHLBI
Reviewer Comments:
  • Though knowledge gains and behavior changes were greater in intervention compared to control group, the statistical analyses did not properly account for the correlation between individuals attending the same school
  • This is a nested randomized trial, so the clustering within schools should be incorporated into the analyses.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? Yes
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? Yes
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? Yes
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? Yes
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? No
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? No
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? Yes
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes