PWM: Physical Activity and Inactivity of Youth (2006)

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

The purpose of this study was to examine the behavioral, socioeconomic and demographic variables that are associated with women’s and children’s adiposity. It was hypothesized that women’s and children’s adiposity may vary by household income.

Inclusion Criteria:

Adult women who completed two days of food recall (both CSFII and DHKS) and school-age children (ages six to 11) who completed two-day dietary recalls as well as the data on household head’s BMI.

Exclusion Criteria:
  • Pregnant or lactating women
  • Individuals missing information
  • Households without a mother.
Description of Study Protocol:


  • Data collected from the 1994-1996 Continuing Survey of Food Intakes by Individuals (CSFII), 1998 CSFII (also known as Supplemental Children’s Survey) and the Diet and Health Knowledge Survey (DHKS), conducted by the US Department of Agriculture (the DHKS, only administered to women, examined knowledge and attitudes toward dietary guidance and health).

Design, Data Collected

  • Household demographics
    • Age
    • Gender
    • Education
    • Race and ethnicity
    • Household income
    • Participation in the Food Stamp Program
    • Type of employment.
  • Food intake questionnaire, two days of food intake by:
    • Type
    • Amount
    • Source
    • Eating occasion of food eaten
    • Percentage of food prepared at home and away
  • Self-reported height, weight, smoking behavior, vitamin use, hours spent watching TV and videotapes, exercise frequency, and whether the respondent is vegetarian
  • DHKS collected data on knowledge and attitudes toward dietary guidance and health.
  • Breakfast is not defined, but breakfast skipping (defined as whether a sample person ate breakfast or not on the recall day) was derived from the eating occasion variable (from CSFII data).
  • Vegetarian diet is not defined.

Statistical Analysis

  • Multivariate regression models (to fit the women and children data)
  • Variance estimation (to incorporate the CSFII sample design)
  • Regression (for high and low income sub-samples).
Data Collection Summary:

Dependent Variables

  • BMI.

Independent Variables

  • Food eaten away from home
  • Beverage consumption (soda, juice)
  • Breakfast skipping
  • Television viewing
  • Vegetarian diet
  • Vitamin use.

Control Variables

  • Age
  • Gender
  • Race
  • Parental/household socioeconomic status.
Description of Actual Data Sample:

  • Initial N: 15,303 individuals and 1,971 children
  • Attrition (final N): 2,419 adult women and 1,651 children
  • Age: Six- to 11-year old children
  • Ethnicity: White, black, Hispanic, and other (ethnically diverse, but not specified in this paper)
  • Location: 50 US states.
Summary of Results:

For Children

  • A strong association was found between maternal and children’s BMI (P<0.01) for all children, regardless of income. Each additional unit of mother’s BMI was linked with a 0.13 to 0.15 higher BMI unit among low- and high-income children, respectively. For the full sample, age, race and gender explained 17% of the variance in children’s BMI; and mother’s BMI contributed an additional 4% of explanatory power. Mother’s BMI explained 2% and 5% of low- and high-income children’s BMI, respectively.
  • Time spent watching television and videotapes was the only lifestyle variable included in the children’s model. This variable was positively associated (P<0.1) with BMI among high-income children, but not among low income children.
  • Each additional year in age correlated with a 0.45 and 0.52 higher BMI unit among low- and high-income children, respectively.
  • Among low-income children, white boys were 0.99 BMI heavier than white girls (P<0.1) and Hispanic girls weight more than white girls by 1.72 BMI units (P<0.05). Among high-income children, white girls had a BMI that averaged 1.09 units greater than Hispanic girls (P<0.1). No significant differences in BMI were found between high-income white and black girls. Boys weigh significantly more than girls among blacks (2.57) and Hispanics (2.15), but not among whites in the high-income sample.
  • There was no significant relationship between any dietary variables and BMI in children.
Author Conclusion:

Among women, the associations between some behavioral and environmental factors and BMI differ by household income. Intervention programs need to target specific eating and physical activity behaviors to promote a healthy body weight.

Funding Source:
Government: USDA
University/Hospital: University of Florida, University of Tennessee
Reviewer Comments:


  • Large national data set
  • Dietary data collected in a standardized way by well-trained interviewers.


  • Surveys were not longitudinal, so regression results imply association, not causality.
  • BMI (height and weight) measured by self-report.
  • Physical activity questions not asked on children’s survey: No controlling for physical activity.

Other Comments

  • Are they using the T-ratio correctly in their interpretation?
  • No figures given for lack of relation in children between BMI and breakfast, sweetened beverages or food away from home (fast food frequency).
  • Overweight and obesity not defined.
  • Juice is not defined and may be included as a “beverage” with soft drinks. The only discussion of juice is in the results for women where the percentage of calories from soft drinks and juice drinks correlated positively with women’s BMI in the full and high income samples, but not among low income women. No discussion of beverages and children is included.
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) N/A
  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) N/A
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.) Yes
  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? ???
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  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.) ???
  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? 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? N/A
  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? N/A
  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? N/A
  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? No
  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? No
  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? ???
  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