A group of occupational epidemiologists were interested in studying whether expo

Question

A group of occupational epidemiologists were interested in studying whether exposure to solvents increased industrial workers’ risk of liver cancer. They identified workers from a single plant without liver cancer, 115 who were exposed to solvents during their job activities and 542 who were not exposed to solvents. They followed the cohort for 10 years and identified new cases of liver cancer for both exposure groups. Among those exposed to solvents, 4 developed liver cancer; among those not exposed to solvents, 3 developed liver cancer. SHOW THE WORK.

1. Create the appropriate 2x2 table for the data in the scenario.

2. Calculate the risk of liver cancer separately for those exposed to solvents and those not exposed. What do you observe?

3. Calculate the risk ratio for the relationship between solvent exposure and liver cancer.

4. Write a 1 sentence numerical interpretation of the risk ratio that you calculated in #26.

5. What is the excess risk of liver cancer among those industrial workers exposed to solvents compared to those not exposed?

6. What is the excess risk of liver cancer in the total population of industrial workers that is associated with the exposure?

7. Why are absolute measures (like the attributable risk and population risk difference) especially useful for assessing public health impact compared to relative measures (like the risk ratio)?

Explanation / Answer

1) Above is the 2X2 CONTINGENCY TABLE.

2) To calculate risks or attack rate seperately :

Risk of liver cancer among exposed to solvents = a/(a+c) = 4/115 = 0.0347 = 3.47%

Risk of liver cancer among not exposed to solvents =b/(b+d) = 3/542 = 0.0055 = 0.55%

Comparitively , risk of liver cancer is high for those who are exposed to the solvents due to chemical reaction.

3) The risk ratio is simply the ratio of these two risks = 3.47/0.55 = 6.3091

4) Numerical interpretation of the risk ratio : Workers who are exposed to solvents were 6.3091 times as likely to develop liver cancer as those who have not exposed to liver cancer.

5) The excess risk of liver cancer among those industrial workers exposed to solvents compared to those not exposed = 3.47% - 0.55% = 2.92%

6) The excess risk of liver cancer in the total population of industrial workers that is associated with the exposure is

(7/657) - (4/657) = 0.0106 - 0.0061 = 0.0045 = 0.45%

7) Absolute risk of a disease is our risk of developing a disease over a time period. We all have absolute risks of developing various diseases such as heart disease , cancer ,stroke etc. The same absolute risk can be expressed in different ways. For example , say you have 1 in 10 risk of developing a certain disease that is 10% risk.

Relative risk is used to compare the risk in two different groups of people. That is smokers have higher risk of developing heart disease as compared to non-smokers.

So medical treatment can be given individually as per the absolute risk for curing or preventing disease.

Therefore, absolute measures (like the attributable risk and population risk difference) especially useful for assessing public health impact compared to relative measures (like the risk ratio).

exposed to solvents Not exposed to solvents Total Develop liver cancer a = 4 b = 3 a+b = 7 = H1 Do not develop liver cancer c = 111 d = 539 c+d = 650 = H0 Total a + c = 115 = V1 b + d = 542 = V0 T= 657

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.