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Science Olympiad» Disease Detectives Event » National Event Exercises
Answer Key: Skin Cancer Epidemiology and Prevention

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Part I
Part II, III, & IV
Part V & VI

Answer Key

  1. Give the definition of “incidence rate.” (3 points — 1 each for explanation of numerator, denominator, and time)

    Answer: Incidence rate is a measure of the frequency with which a health problem or health event (such as a new injury or case of illness) occurs in a population. In calculating incidence, the numerator is the number of new cases occurring in the population during a given period of time, and the denominator is the total population at risk during that time.

  2. For some subgroups, the incidence rates appear to have increased overall in the past 20 years. Give two reasons for this apparent increase. (2 points — 1 for each valid reason)

    Answer: Factors that could contribute to the rise in rates include
    • increased exposure to UV radiation as a result of more people being exposed to the sun 
      (Note: This is the most important reason.);
    • ozone depletion; 
    • heightened awareness among health care providers;
    • increased reporting (improved surveillance); and
    • people living longer — increased survival.

  3. Referring to Figure 1, give the 1998 incidence rate for the following groups: (8 points — 2 for each rate. Estimates are acceptable; however, units must be cited. Take off 1 point for each rate without units.)

    • White Men 19.3 per 100,000 persons
    • White Women 13.6 per 100,000 persons
    • Black Men 1.1 per 100,000 persons
    • Black Women 1.0 per 100,000 persons 

  4. Give two possible reasons for the observed large differences in incidence rates between races. (2 points — 1 for each valid reason)

    • Racial and ethnic differences in observed rates are mostly due to skin color, which is determined by the amount of melanin produced by skin cells called melanocytes. Melanin also protects the skin from damage by UV radiation. Although darkly pigmented people (e.g., African-Americans, Asians, Hispanics) develop skin cancer on sun-exposed sites at lower rates than lightly pigmented people, UV exposure still increases their risk of skin cancer.
    • Different cultures may have different prevention behaviors.
    • Exposure may tend to be longer and more intense in some cultures than in others.
    • Diagnosis may be more difficult when skin is highly pigmented.

  5. The rates in Figure 1 are age-adjusted. (1) Define “age adjustment” and (2) explain why Disease Detectives would use age-adjusted rates. (2 points — 1 for each part of the answer)

    • Age adjustment is a statistical technique that uses the age distribution of a standard, or reference, population to adjust crude rates. Or, if actual methods for age adjustment are given: multiplication of an observed age-specific rate in each of two comparison groups by a standard population.
    • Age-adjustment eliminates the effect of age on the data being compared, thus allowing Disease Detectives to compare incidence rates for different subgroups which otherwise may have different age distributions.

  6. Define “mortality rate.” (3 points — 1 for each of the key elements)

    Answer: Mortality rate is the rate of occurrence of death in a defined population during a specified time interval. (Note: The student’s answer should contain such key words as “deaths,” “population at risk,” and “over time.”)

  7. Referring to Figure 2, give the 1998 mortality rates for the following groups: (8 points — 2 for each rate. Estimates are acceptable; however, units must be cited. Take off 1 point for each rate without units.)

    • White Men 3.7 deaths per 100,000 persons 
    • White Women 1.6 deaths per 100,000 persons
    • Black Men 0.3 deaths per 100,000 persons
    • Black Women 0.4 deaths per 100,000 persons

  8. Note the difference in mortality rates between white men and white women. Give two possible reasons for this difference. (2 points — 1 for each valid reason)

    Answer: Several explanations are possible for the higher rate among white men:
    • White women may be more aware than white men of skin cancer risk and, therefore, may have protected their skin better in childhood and adulthood.
    • Diagnosis may take place at a later stage for white men than for white women.
    • Genetic determinants may differ between white men and women.
    • Health care workers may be more responsive to suspicious lesions in women and, therefore, have greater tendency to biopsy or excise tissue from women.
    • Men may have a higher prevalence of exposure because of occupational patterns.

  9. Using the map (Figure 3), list two geographic areas with high melanoma death rates. (2 points — 1 for each correct area)

    Answer: Coastal, Southeast, West, and Texas. A north-south differential was seen among white men with lower rates in the North and higher rates in the southeastern and south-central regions.

  10. Referring to Figure 3, give two possible reasons for higher mortality in the places that you listed in the Question 9. (2 points — 1 for each valid reason)

    • Recreational exposure may be different for coastal areas (e.g., beach exposure).
    • Occupational exposure may be higher in Texas.
    • Personal awareness of risk (and therefore preventive behaviors) may differ as a function of regional prevention programs.
    • General gradient by latitude that may reflect intensity of exposure, with some exceptions. (Note: The map is for white men only, so “differences in skin color/pigmentation” is not a valid answer.)
    • Differences due to health care availability.

  11. Using Figure 4, give the five states with the highest mortality rates for white men? (5 points — one for each correct state)

    • Delaware
    • Mississippi
    • Tennessee
    • South Carolina
    • Georgia

  12. Give two reasons why melanoma mortality rates might be higher for white men in Delaware than for men in neighboring states and some states in the south. (2 points — 1 for each valid reason)

    Answer: White men in Delaware might be
    • genetically predisposed to have fair skin or other traits that make them more susceptible to skin cancer;
    • more likely to engage in behaviors that put them at increased risk of melanoma (e.g., repeated exposure);
    • less likely to use protective measures;
    • less likely to receive health care that adequately addresses skin cancer.

  13. Give two reasons why Disease Detectives would be interested in monitoring the sunscreen use of high school students? (2 points — 1 for each valid reason)

    Answer: Overexposure to the sun as a child or teenager is an important factor in the development of skin cancer later in life. Because they are making their own behavioral decisions, teenagers should be especially encouraged to take precautions against skin cancer. Monitoring their sunscreen use helps scientists
    • target programs toward subgroups that have the riskiest behavior;
    • see if and how risky health behaviors are related;
    • start up, monitor, and improve policies and programs to reduce unprotected UV exposure among youth.

  14. Define “prevalence” as used in Table 1. (3 points — 1 each for indication of numerator, denominator, and time)

    Answer: Prevalence as used in Table 1 is the rate, or proportion, of people in a population at a given time who have a certain disease, chronic condition, injury, or attribute. We can calculate prevalence at a particular point in time (point prevalence) or during a specified period of time (period prevalence).

  15. Using Table 1, determine the prevalence for frequent (“most of the time” or “always”) sunscreen use. (2 points)

    Answer: 13.3% of students reported frequent sunscreen use when they are outside for more than one hour on a sunny day.

  16. Use the data in Table 1 to identify three characteristics of a hypothetical student who is least likely to use sunscreen. (3 points — 1 for each characteristic)

    Answer: Give credit for
    • “Older” or “age > 18” (no credit for grade)
    • Black
    • Male

  17. Use the data in Table 2 to identify three behaviors with which sunscreen use is positively associated. (3 points — 1 for each correct behavior)

    Answer: Teens who reported using sunscreen were also likely to report
    • not carrying a weapon
    • wearing a bike helmet
    • wearing a seat belt
    • not driving after drinking
    • not smoking
    • not drinking 
    • not using marijuana 
    • not being sexually active
    • being neither overweight nor at risk of being overweight
    • eating more than 5 servings of fruits and vegetables per day
    • being vigorously and moderately physically active

  18. Using sunscreen is one way to reduce ultraviolet (UV) exposure. Other sun-safety measures include wearing hats and long-sleeved clothing and limiting time spent in the sun during midday. List three ways to encourage students to adopt any of these behaviors. (3 points — 1 for each valid strategy)

    • Introduce sun-safety education into curriculum.
    • Encourage environmental changes such as planting trees, building shade structure.
    • Encourage policies that will encourage you to play inside when it is sunny.
    • Encourage policies that facilitate preventive measures, e.g., wearing hats outdoors.
    • Encourage parents and teachers to practice sun-safe behavior themselves.

  19. List two limitations to the YRBS that you noted while using the data to study sun protective practices. (2 points — 1 for each correct limitation)

    • Data is self-reported.
    • Use cannot be confirmed or validated.
    • Generalizability of the results is limited because the survey includes only kids in schools and in regular classrooms.
    • Reporting or information bias is possible (e.g., students may give answers they believed the teacher or interviewer want to hear).
    • Some of the terms in the survey are ambiguous (e.g., “sometimes” or “rarely”).
    • The study has a very short observational period (30 days before the survey).

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This page last reviewed August 27, 2004

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