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Science Olympiad » Disease Detectives Event » National Event Exercises
Epidemic of Overweight


   

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Epidemic of Overweight Exercise
 

Answer Key

1. To identify people with disease or health conditions in an epidemiologic investigation, disease detectives frequently use a case definition. List the basic elements of case definitions.

Answer (4 points, 1 for each element)

  • Clinical information on the disease
  • Information about location or place
  • Characteristics of the people affected
  • Time during which the outbreak occurred

2. Define prevalence rate.

Answer (3 points)
Prevalence rate is a measurement of the frequency with which a health problem or health event (e.g., obesity or illness) exists in a population during a given time. In calculating prevalence, the numerator is the total number of cases existing in the population during the time in question, and the denominator is the total population at risk (including people who have the condition) during that time.

Note: Look for key words such as existing (total) cases, population at risk, over time. (1 pt each for these 3 concepts: numerator = number of cases, denominator = population at risk, time aspect = specific time period).

3. You observe from Figure 1 that, overall, prevalence of overweight has increased in the past 25 years. Give two reasons why this apparent pattern may not reflect a true increase in prevalence.

Possible Answers (2 points, 1 for each reason)

  • Change in case definition
  • Change in measurement
  • Change in ascertainment
  • Change in sample characteristic

4. Supposing that Figure 1 reflects true changes in prevalence over time, list three possible explanations for this trend.

Possible Answers (3 points, 1 for each explanation)

  • Caloric intake greater than caloric expenditure through physical activity
  • Poor diet (e.g., dietary intake high in calories from sugar and fat
  • Cultural or social pressure to gain weight
  • Decreased exercise because of lack of encouragement or opportunity (e.g., reduction in school PE resources, sports programs, community elimination of bike paths, closed stairwells in public buildings, lack of initiative (“couch potato syndrome”)
  • Poor urban planning or neighborhood safety

5. For respondents aged 12-19 years in all racial and gender groups, which single group of those listed below had the greatest relative increase between the 1988-1994 and 1999-2000 surveys? Show your calculations for each category and then circle the correct category.

Answer (7 points, 1 for each calculation and 1 for answer; calculation should show numerator, denominator and quotient.)

a) White, non Hispanic boys 12.8/11.6 = 1.10
b) Black, non Hispanic boys 20.7/10.7 = 1.93
c) Mexican boys 27.5/14.1 = 1.95
d) White, non Hispanic girls 12.4/8.9 = 1.39
e) Black, non Hispanic girls 26.6/16.3 = 1.63
f) Mexican girls (unstable) 19.4/13.4 = 1.44

For overall answer, accept category b, c, or both.

6. Give a likely explanation for the missing data in Table 1.

Possible Answers (1 point)

  • Changing definition of racial/ethnic categories
  • Data may not have been collected.

7. Name the study design used for NHANES.

Answer (1 point)
Cross-sectional or survey

8. List 2 advantages and 2 disadvantages of this study design for understanding the problem of overweight in children and adolescents. (Note: A disadvantage is not merely the opposite of an advantage).

Answer (4 points, 1 for each valid answer)
Advantages: quick, relatively cheap, allows collection of multiple covariates
Disadvantages: cannot assess causality, confounding, bias.

9. What conclusions can you draw by taking into account data from Figure 1 and Figure 2 together? Justify your answer.

Answer (2 points, 1 for conclusion and 1 for justification)
None. There is no data on individuals. The two figures cover different periods. (Might be used to generate hypothesis that other unhealthy behaviors are related to overweight.)

10. Name the study design used for the Bogalusa Study.

Answer (1 point)
Cohort, prospective, or longitudinal

11. List 2 advantages and 2 disadvantages of this study design in studying the health effects of overweight in adolescents. (Note: A disadvantage is not merely the opposite of an advantage).

Answer (4 points, 1 point for each valid answer)
Advantages:
More likely to support causality
Reduces some forms of bias, controls confounders

Disadvantages:
Expensive
Lengthy
Study subjects lost to follow-up
Bias due to multiple measures on risk .

12. What main conclusion can you draw about the relationship between childhood BMI and adult BMI? Provide data to support your conclusion.

Answer (2 points, 1 for conclusion and 1 for support data)
Childhood overweight is a risk factor for adult obesity; this relationship is direct. Of the overweight kids, 77% remained obese as adults; only 7% of normal weight kids were obese as adults.

13. Based on your analysis of the epidemiology of overweight and obesity in Part A, list three strategies that families could implement in their homes to prevent this problem among children and adolescents.

Answer (3 points, 1 for each valid strategy)

  • Healthy meals and snacks
  • Family physical activity
  • Restrictions on TV/Video game time
  • Parent role models
  • Social support for physical activity

14. Based on your analysis of the epidemiology of overweight and obesity in Part A, list three strategies that schools and communities could implement to prevent this problem among children and adolescents.

Answer (3 points, 1 for each valid strategy)

  • Inexpensive, healthy choices for school food and vending machines
  • Nutrition and cardiovascular education
  • Recreational facilities
  • Physical activity requirements

15. The health department asks you, a disease detective, to design a study to determine whether any of these intervention methods work to decrease overweight in adolescents.

a) Name the study design that you would use.

Answer (1 point)
Randomized control trial, cohort, case control

b) List four elements of the study design that you have just named that would be critical to a valid evaluation of the effectiveness of the intervention.

Study Design

Randomized Control Trial

Cohort Case-Control
Elements
Randomization

X

-- X
Determine exposure/outcome X X X
Measure exposure/outcome X X X
Study horizon X X --
Lost to follow-up X X --
Non-Response -- -- X
Selection of comparison/control group -- -- X
Systematic/standardized data collection X X X
Response rate X X X
Acceptable methodology X X X
Confounders X -- X

Bias — must specify type and relation to study design

 

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This page last reviewed August 27, 2004

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