





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)
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)
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)
5. For respondents aged 1219 years in all racial and gender groups, which single group of those listed below had the greatest relative increase between the 19881994 and 19992000 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)
7. Name the study design used for NHANES.
Answer (1 point)
Crosssectional 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 followup
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)
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)
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.
