A public health department conducts a 10-year prospective cohort study to evaluate the ass… — USMLE Step 2 CK

A public health department conducts a 10-year prospective cohort study to evaluate the association between a diet high in ultra-processed foods and the development of metabolic syndrome. The study enrolls 10,000 healthy adults without pre-existing metabolic conditions. Participants are categorized into two groups based on detailed dietary questionnaires. Over the 10-year follow-up period, the occurrence of new metabolic syndrome diagnoses is recorded. The results are summarized in the table below:

Dietary Pattern	Developed Metabolic Syndrome	Did Not Develop Metabolic Syndrome	Total
High ultra-processed food consumption	400	4,600	5,000
Low ultra-processed food consumption	150	4,850	5,000

Based on these study results, what percentage of metabolic syndrome cases among the participants with high consumption of ultra-processed foods can be attributed to their dietary pattern?

Answer: 62.5 %

Answer

62.5

The question asks for the percentage of disease cases among the exposed population that can be specifically attributed to the exposure. This is the definition of the Attributable Risk Percent (ARP), also known as the etiologic fraction. It is calculated using the formula:

ARP = \frac{I_{exposed} - I_{unexposed}}{I_{exposed}} \times 100

, or alternatively

ARP = \frac{RR - 1}{RR} \times 100

. Using the incidence data from the table:

I_{exposed} = 0.08

and

I_{unexposed} = 0.03

. Therefore,

ARP = \frac{0.08 - 0.03}{0.08} \times 100 = 62.5\%

Step-by-Step Solution

Calculate the incidence of metabolic syndrome in the exposed group (high ultra-processed diet).

\frac{400}{5,000} = 0.08

The incidence in the exposed group (

I_{exposed}

) is required to determine the baseline risk associated with the exposure.

Calculate the incidence of metabolic syndrome in the unexposed group (low ultra-processed diet).

\frac{150}{5,000} = 0.03

The incidence in the unexposed group (

I_{unexposed}

) provides the baseline risk without the primary exposure.

Calculate the Attributable Risk (AR).

0.08 - 0.03 = 0.05

AR represents the excess absolute risk of the disease directly tied to the exposure.

Calculate the Attributable Risk Percent (ARP).

(\frac{0.05}{0.08}) \times 100 = 62.5\%

ARP represents the proportion of disease cases among the exposed that are specifically attributable to the exposure.

Key Concept

Attributable Risk Percent (ARP)

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