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

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To evaluate the impact the Know Your Body (KYB) comprehensive school health education program in a sample of 1st – 6th grade students from New York City, using two analytic strategies: a longitudinal cohort and a posttest only cohort.

Inclusion Criteria:
Students from grade 1-4 with consent.
Exclusion Criteria:
Students with learning disabilities.
Description of Study Protocol:

3 of the 4 New York City schools received the KYB program and the 4th served as a comparison school. A 5th school, located near Houston, Texas served as a second comparison school. KYB program was implemented for ~ 1 ½ years.

Classroom curriculum included grade-specific teacher manuals and student activity books. Teachers were asked to utilize the curriculum at least once a week for 30-45 minutes during the entire school year.

School-wide activities included a series of school-wide health activities and environmental modifications. In each school, the project coordinator worked with district and school level food service personnel to modify the school cafeteria with an overall goal of increasing fiber and decreasing fat content of the foods served. Examples: addition of salad bars, increasing the visibility and availability of low-fat milk & offering heart healthy entrée options. Other activities included peer leader training, student health committees, food tasting parties, drug and nutrition poster and essay contests, student aerobics, & special health lectures.

Data Collection Summary:


  • Total cholesterol (nonfasting finger stick samples),
  • BMI (measured height & weight),
  • Health knowledge (age-appropriate instruments - content of the knowledge items was based upon the learner outcome goals delineated in each module of the curriculum,
  • Health attitudes & Self-efficacy scales (measured in grades 4-6 only),
  • Dietary Intake: dairy, meat fruit, vegetables, high-fat & heart-healthy foods (non-quantitative food frequencies).


Degree of exposure to the program (high exposure, moderate exposure, low exposure)

Control Variables

All analyses controlled for race and age, while longitudinal analyses controlled for baseline values.


  • age,
  • sex,
  • grade,
  • race
  • baseline value/score.

Statistical Analysis

Multivariate analysis of covariance and trends in means across intervention groups were assessed using linear regression.

Description of Actual Data Sample:

Original Sample (Longitudinal cohort): Of the 3,423 1st-6th grade students from New York City eligible for the study in 1987-1988 baseline, questionnaire and/or screening data were obtained from 2,973 (87%). Follow-up data were obtained from 1,209 (41%) of these students.

Location: inner New York City

Race/Ethnicity: Predominantly Hispanic community – 60%, primarily Dominican & Puerto Rican, 23% Black, 11% white 9including Asian) & 5% other.

SES: Lower socioeconomic status community.

57% were female & the mean age at posttest was 10 years.

Summary of Results:

At baseline, the children from the intervention and comparison schools did not significantly differ with regard to sex, total cholesterol, systolic blood pressure, body mass index, health attitudes, self-efficacy, & the remaining dietary indices.

Longitudinal cohort results

(program impact was assessed among students for whom baseline and 3-year posttest values were available)

Total cholesterol & Blood Pressure

Students in the high exposure group had significantly lower total cholesterol and systolic blood pressure values than the comparison group (p<0.05).

When the intervention group when combined, they had significantly lower total cholesterol (p=0.03) and systolic blood pressure (p=0.003) levels than comparison students.

Health Knowledge

Mean health knowledge was significantly (p<0.05) higher in the comparison group than each of the 3 intervention groups.


Posttest values for BMI did not significantly differ between any of the four groups.

Dietary Indices

Posttest values for 5 of the 6 dietary indices were in the criterion direction (higher for vegetable and heart healthy indices and lower for meat, diary, and dessert indices) although these differences did not achieve statistical significance.

Posttest only cohort results

(program impact was assessed by examining data from all students who participated in the Year 3 posttest.

Cholesterol & Blood Pressure

Students in the posttest only cohort who had a high implementation teacher during Year 3 had significantly (p<0.05) lower total cholesterol & systolic BP values than students in the comparison group.

When the 3 intervention schools were combined, they had significantly lower systolic blood pressure levels (p<0.001) than comparison students.

Health knowledge

They (high implementation) also had higher health knowledge scores than students in the comparison group.

Dietary indices

These students (high implementation) reported significantly greater consumption of vegetables and heart healthy foods and significantly lower consumption of meat and desserts.

Posttest values for fruit and dessert intake, between high exposure and comparison students were in the criterion direction (i.e. higher for fruit and lower for desserts) although these differences did not achieve statistical significance.

When the 3 intervention school were combined, they reported significantly lower intakes of dessert (p=0.021) and greater intake of vegetables (p<0.01) and heart healthy foods (p=0.007).


Posttest values for BMI between high exposure and comparison students were not significantly different.

Author Conclusion:

(author’s words from the discussion)

"While several methodologic limitations may have influenced study outcomes, these data nonetheless appear to confirm that the Know Your Body program can have a significant positive impact on the knowledge, behavior, and several risk factors of students in primary grades and that efforts to disseminate & evaluate school health education programs should include strategies to monitor & enhance teacher implementation."

Funding Source:
Foundation associated with industry:
Reviewer Comments:

Know Your Body is a school-based approach to the primary prevention of heart disease. Health related outcomes were positively effected by the intervention without a change in health knowledge - may be more of an effect of school food service.

Measurement error could also account for lack of program effects of health knowledge. Evaluation instruments used generic rather than curriculum specific terminology may have contributed to the lack of detecting program effects.

Only 12% of the longitudinal cohort could be classified as high exposure which raises questions about the construct validity of the study.

Schools were not randomly assigned to condition.

High attrition rate 59%, seen in the longitudinal cohort.


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) N/A
  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")? Yes
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? Yes
5. Was blinding used to prevent introduction of bias? ???
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? No
  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? ???
  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? Yes
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? N/A
  6.6. Were extra or unplanned treatments described? N/A
  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? Yes
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? Yes
  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? Yes
  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)? N/A
  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