## **Core Concept**
The core concept being tested here is the calculation of **incidence** of a disease, specifically dental caries, in a population over a specified period. Incidence refers to the number of new cases that develop in a specified time period among a population at risk.

## **Why the Correct Answer is Right**
To calculate the incidence of dental caries from 2000 to 2003, we first need to understand the given data: the prevalence in 2000 was 18%, and in 2003 it was 38%. Prevalence includes both new and existing cases. The incidence rate can be calculated using the formula: Incidence = (Number of new cases / Population at risk) * 100. Here, the population at risk in 2000 would be those without dental caries, which is 100% - 18% = 82%. The new cases from 2000 to 2003 would be 38% - 18% = 20%. So, the incidence = (20 / 82) * 100.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not accurately reflect the calculation of incidence. Without the actual numbers, we can't directly calculate, but we know incidence is about new cases over at-risk population.
- **Option B:** Similarly, this option does not correctly represent the incidence calculation based on provided data.
- **Option D:** This option is incorrect as it likely misrepresents the formula or the data provided.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **incidence** reflects the rate of new disease occurrences, whereas **prevalence** reflects the total burden of disease in a population at a given time. For calculating incidence, one must consider the population at risk (those without the disease) at the beginning of the study period.

## **Correct Answer:** C. 24.4%