**Question:** Incidence rate of lung cancer among smokers is 8 per 1000 and among non-smokers is 1 per 1000. Population attributable risk is -

A. Reduction in incidence rate
B. Increase in incidence rate
C. Relative risk
D. Attributable risk

**Core Concept:**
The concept being tested in this question is the calculation of population attributable risk (PAR), which is used to assess the proportion of a disease in a population that can be attributed to a specific risk factor, like smoking. In this case, we are considering the difference in incidence rates of lung cancer between smokers and non-smokers.

**Why the Correct Answer is Right:**
The correct answer is D. Attributable risk because it measures the proportion of disease cases that would not occur in a hypothetical situation where the risk factor (smoking) is eliminated from the population. In this scenario, the PAR for lung cancer would be calculated as:

PAR = (Incidence rate among smokers - Incidence rate among non-smokers) / Incidence rate among smokers
PAR = (8/1000 - 1/1000) / 8/1000
PAR = 7/1000 / 8/1000
PAR = 1

**Why Each Wrong Option is Incorrect:**
A. Reduction in incidence rate: This option does not address the proportion of disease cases that would occur if the risk factor is eliminated.
B. Increase in incidence rate: This option is the opposite of the correct answer and does not address the proportion of disease cases if the risk factor is eliminated.
C. Relative risk: Relative risk compares the risk between two groups but does not represent the proportion of cases that would occur if the risk factor was eliminated.

**Population attributable risk explanation:**
The population attributable risk is a useful tool in epidemiology to estimate the impact of a risk factor on a specific disease incidence. It helps to assess the proportion of cases that would not occur if the risk factor were eliminated from the population. In this case, the attributable risk of lung cancer due to smoking is 7 out of 1000, which means that if smoking were eliminated, 7 fewer cases of lung cancer would occur per 1000 people.

**Clinical Pearl:**
Understanding population attributable risk helps healthcare professionals and policymakers to evaluate the burden of a specific disease due to a risk factor and estimate the impact of interventions targeting that risk factor. In this example, the attributable risk of lung cancer due to smoking demonstrates the potential decrease in disease cases if smoking were eliminated from the population. This information is vital for public health strategies focused on reducing tobacco use, such as promoting smoking cessation campaigns and implementing smoke-free policies.