Skip Navigation Links
Centers for Disease Control and Prevention

 CDC Home Search Health Topics A-Z
Office of Surveillance, Epidemiology, and Laboratory Services

EXCITE Home  |  Contact Us
Menu Contents

Science Olympiad » Disease Detectives Event » National Event Exercises
Answer Key: Potential Health Hazards Associated with the Use of Cellular Telephones

Problem Set 1

See Also...
Problem Set 1
Problem Set 2

Answer Key

  1. 1 point for each, up to a maximum of 2: ecologic, cohort, cross-sectional, case control

  2. To minimize study bias and increase generalizability of results.

  3. Part (a) and part (b):
    1. Case definition

    2. A patient older than age 18, admitted between 1994 and 1998 to one of three participating hospitals with primary malignant brain tumor. (Students can go for 3 of 4 possible points)

  4. Consult Table 1 below.

    Table 1: Characteristics* of persons included in the investigation of cell phone use and brain cancer

Characteristic Brain Cancer No Brain Cancer Answer OR
Use of hand-held cell phone      
Ever used 308 358  0.8
Never used 471 440  
Average daily use      
>15 minutes 35 51  0.7
<15 minutes 103 117  0.9
Never/rarely 637 625  
Cumulative use       
>500 hours 18 27  0.7
101 to 499 hours 34 27  1.2
13-100 hours 47 58  0.8
<13 hours 39 55  0.7
Never/rarely 637 625  

*Categories within each characteristic are mutually exclusive.
Some characteristics were not measured for all study participants.

    1. There is no evidence of a relation between exposure/use and risk of disease. Some students may conclude a protective effect in the absence of significance testing.

    2. Because this is a case/control study, we used an odds ratio to assess the risk between use of cell phones and occurrence of brain cancers. Calculations showed the odds ratios to be 1.0 or less, indicating no increased risk of brain cancers associated with use of cell phones.

      This problem required seven calculations of odds ratios, shown on the table above. For example, to calculate the risk associated with average daily use, one would first calculate odds of use more than 215 minutes compared to never/rarely:

      Odds ratio (associated with average daily use >=15 minutes) = ad/bc = (35) (625)/(51)(647) = 0.7.

      Odds ratio (associated with average daily use < 15 minutes) = ad/bc = (103) (625)/(117)(647) = 0.9.

      Clarifying note to students and teachers: it is important in stratified tables such as this that the calculation of odds ratio always use the referent category. In this instance, the referent category is "never/rarely" (i.e., the baseline of no exposure to cell phones).

    3. Case-control study

    4. Odds-ratio

  1. Recall bias due to inability to capture historical patterns of use or memory impairment due to disease or time lapse. Ascertainment bias, because people who are more likely or less likely to use cell phones were differentially included in or excluded from the study (e.g., due to socioeconomic factors). Information bias, if investigators’ bias toward expected results influenced data collection.

  2. Environmental: Long-term (induction periods use, changing phone technology.

    Behavior: changing patterns in use.

Back to Problem Set 1

Problem Set 2

  1. Consult the Table 1.
    1. The data do not support a causal association: there is no comparison group.

    2. The data can be used for descriptive purposes only, for generating hypotheses. They can be used to show whether the study group is comparable to other populations. Student gets no points for concluding that %x > %y.

  2. Younger drivers, those who have not graduated from high school, limited cell phone experience. If student mentions only 1, it should be education. One point for highest only; 2 points for more than one. In explanation, 1 point for stating that RR was elevated. Additional point if clarified meaning of relative risk as probability of having a collision when using a cellular telephone at any time (during a 10-minute interval) as compared with the probability of having a collision when not using a cellular telephone (at any time during that interval).

  3. Agent: agent necessary to cause the health event (e.g., mechanical energy of car).

    Host: person or organism susceptible to the agent (e.g., driver).

    Environment: conditions of influences not part of agent/host which influence their interaction (e.g., conditions of the roadway, conditions in the interior of the vehicle).

  4. Student should mention 2 of the following:
    Those who did not consent to participate.

    Variability in driving patterns.

    Geographical factors.

    Confounding (e.g., emotional stress).

    Crash due to another driver.

    Accuracy of phone/accident time data (e.g., excess phone use may have been due to drivers calling to report car crash; the cause-effect relation may be reversed).

  5. Legislative: regulatory or restrict for certain populations.

    Behavioral: individual responsibility, minimize use.

    Some students may conclude lack of sufficient evidence for causation.

    No points for hands-free cell phone use while driving.

Back to Problem Set 2


Criterion name and definition Brain Cancer Motor Vehicle Crashes
The cause/exposure must precede the effect/outcome.
Not addressed Yes, in table
Observation of the association must be repeatable in different populations at different times.
No or yes (anecdotal reports) No, single study
Coherence, 1-1 relationship
Exposure is always associated with the outcome; outcome is always caused by the specific exposure.
No No
Strength of association
The relationship is clear; the risk estimate is high.
Yes Yes
Biologic plausibility
The explanation must make sense biologically.
Yes or no Yes, distraction
Dose/response (biologic gradient)
There is a dose/response relation; increasing risk is associated with increasing exposure.
Yes Yes

Back to Tiebreaker

Back to Introduction

This page last reviewed August 27, 2004

EXCITE Home | Contact Us
CDC Home | Search | Health Topics A-Z
Privacy Policy | Accessibility

United States Department of Health Human Services
Centers for Disease Control and Prevention
Office of Surveillance, Epidemiology, and Laboratory Services
Scientific Education and Professional Development Program Office