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Question

Difficulty: HardMeasures of Disease Frequency and Association

A prospective cohort study is conducted to evaluate the association between a diet high in ultra-processed foods and the development of colorectal cancer. The investigators enroll 50,000 healthy adults aged 45 to 60 years. At baseline, participants complete detailed dietary questionnaires and are categorized based on their dietary patterns. The high ultra-processed food (UPF) consumption group includes 10,000 participants, while the low UPF consumption group includes 40,000 participants.

All participants are followed for 15 years. During the follow-up period, 400 incident cases of colorectal cancer are diagnosed among the participants in the high UPF group. In the low UPF group, 400 incident cases of colorectal cancer are diagnosed.

Based on the study results, what percentage of the colorectal cancer cases among the participants with high ultra-processed food consumption is attributable to their high UPF diet?

Answer: 75 %

Answer

The attributable risk percent is 75%.
The question asks for the percentage of disease among the exposed group (high UPF consumption) that is attributable to the exposure. This is the definition of Attributable Risk Percent (ARP), also known as the etiologic fraction in the exposed. It is calculated by determining the excess risk in the exposed group (Attributable Risk, or Ie−IuI_e - I_u) and dividing it by the total risk in the exposed group (IeI_e). First, calculate the incidence in the exposed (IeI_e): 400/10,000=0.04400 / 10,000 = 0.04. Next, calculate the incidence in the unexposed (IuI_u): 400/40,000=0.01400 / 40,000 = 0.01. The excess risk (AR) is 0.04−0.01=0.030.04 - 0.01 = 0.03. Finally, divide the excess risk by the total risk in the exposed: 0.03/0.04=0.750.03 / 0.04 = 0.75, or 75%75\%.

Step-by-Step Solution

1
Calculate the incidence rate in the exposed group (IeI_e).
Ie=400/10,000=0.04I_e = 400 / 10,000 = 0.04 (4%4\%)
This establishes the baseline absolute risk of developing the disease for those with the exposure.
2
Calculate the incidence rate in the unexposed group (IuI_u).
Iu=400/40,000=0.01I_u = 400 / 40,000 = 0.01 (1%1\%)
This establishes the background risk of the disease that occurs regardless of the exposure.
3
Calculate the Attributable Risk Percent (ARP) in the exposed.
ARP=0.04−0.010.04×100=75%ARP = \frac{0.04 - 0.01}{0.04} \times 100 = 75\%
ARP quantifies the percentage of cases in the exposed population that can be attributed directly to the exposure.

Key Concept

Attributable Risk Percent (ARP)
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Topics

Measures of Disease Frequency and Association

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