Pediatric Weight Management

Pediatrics and Physical Activity


Hernandez B, Gortmaker SL, Colditz GA, Peterson KE, Laird LM, Parra-Cabrera S. Association of obesity with physical activity, television programs and other forms of video viewing among children in Mexico City. International Journal of Obesity and Related Metabolic Disorders 1999;23:845-854.

PubMed ID: 10490786
Study Design:
Cross-Sectional Study
D - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

The objective of this study is to document the prevalence of obesity and to assess the association between TV program viewing and other forms of video viewing – video games or viewing of videos on VCR – and physical activity with the prevalence of obesity among children 9-16 years old in low and middle income town in the Mexico city area.

Inclusion Criteria:

Not specified

Exclusion Criteria:

Not specified

Description of Study Protocol:

Measures of height, weight, and triceps skinfolds were obtained. During that same visit, hours of TV and video viewing as well as physical activity were assessed by questionnaire.

Statistical Analyses:

Prevalence rates of obesity by covariates were studied.


Tv viewing and other video viewing, physical activity, energy intake and percentage of energy from fat were divided in quartiles for the estimation of crude and adjusted OR for obesity.

Logistic Regression models were also fitted with TV programs, other video viewing and physical activity as continuous variables, and to separate moderate and vigorous activity.

Data Collection Summary:

Dependent Variables

  • Obesity – BMI and triceps skinfold greater than or equal to 85th percentile.

Independent Variables

  • TV and video viewing (hours per day)
  • Physical activity – Hours per day


  • Dietary intake
  • Consumption of snacks while watching TV
  • Perception of parent’s weight status
  • Age
  • Gender
  • Maturation
Description of Actual Data Sample:

Participants were from 7 different schools in a low and a middle income town. 3 schools within these areas were selected.  All students in 5th to 8th grade were invited to participate.  764 children were invited, 712 participated (93%).  Final sample consisted of 461 children (64%).

Summary of Results:

In the analysis conducted with the TV viewing and activity variables categorized in quartiles, no significant odds ratios for obesity were found for TV program viewing.  However, odds ratios showed a significant increasing trend (1.16 for 1-2.1 hours of TV, 1.44 for 2.2 to 3.1 hours of Tv, 1.69 for more than 3.1 hours per day) compared with children who watched less than 1 hour per day (B = .17, P = .0001).

The Odds of obesity were reduced among children in the fourth quartile of PA compared with those in the first quartile (B = -.11, P = .01).  These associations followed a similar pattern among children in elementary and middle school, boys and girls and among children with or without a mother perceived as obese.

With OR adjusted for obesity, a significant OR for obesity by time dedicated to TV program viewing was found.  Compared with children who watched less than 1 hour per day children who watched more than 3.1 hours per day had 1.87 greater odds of being obese.

In the multivariate model, the odds of obesity increased by 12% for each additional hour of TV program viewing (OR = 1.12) and decreased by 10% for each additional hour of moderate/vigorous activity (OR = .90). 

When fitting the model with vigorous and moderate activity separately, the risk of obesity decreased by 20% for each hour of practice of vigorous activity (OR = .80).

Author Conclusion:

Only TV viewing, not other forms of video viewing, were associated with an increased risk of obesity.

Practicing physical activity, particularly vigorous activity, was a protective factor for obesity.

Overall conclusion:

Reducing TV program viewing and increasing time dedicated to physical activity were identified as strategies to prevent obesity in this population.

Funding Source:
Government: Ministry of Education of Mexico
Reviewer Comments:


  • Cross-sectional – therefore no causation can be determined.
  • BMI has limitations and the authors were not able to use a more precise measure of adiposity. 
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? N/A
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? N/A
  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? N/A
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? N/A
  1.3. Were the target population and setting specified? N/A
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? N/A
  2.2. Were criteria applied equally to all study groups? N/A
  2.3. Were health, demographics, and other characteristics of subjects described? N/A
  2.4. Were the subjects/patients a representative sample of the relevant population? N/A
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? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  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? N/A
  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? N/A
  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%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? N/A
  4.4. Were reasons for withdrawals similar across groups? N/A
  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? N/A
  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.) N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  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? N/A
  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? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? N/A
  7.2. Were nutrition measures appropriate to question and outcomes of concern? N/A
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? N/A
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? N/A
  7.5. Was the measurement of effect at an appropriate level of precision? N/A
  7.6. Were other factors accounted for (measured) that could affect outcomes? N/A
  7.7. Were the measurements conducted consistently across groups? N/A
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? N/A
  8.2. Were correct statistical tests used and assumptions of test not violated? N/A
  8.3. Were statistics reported with levels of significance and/or confidence intervals? N/A
  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)? N/A
  8.6. Was clinical significance as well as statistical significance reported? N/A
  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? N/A
  9.2. Are biases and study limitations identified and discussed? N/A
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? N/A
  10.2. Was the study free from apparent conflict of interest? N/A