**Core Concept**
The age and sex structure of a population is an important demographic characteristic that can be described by a statistical model, reflecting the distribution of individuals by age and sex within a population.

**Why the Correct Answer is Right**
The correct answer is a **Pareto Chart**. A Pareto chart is a type of bar chart that displays the distribution of a population by age and sex, with the most common categories appearing on the left side. It is a powerful tool in epidemiology and public health, allowing researchers to identify trends and patterns in population demographics. The chart is named after Vilfredo Pareto, who first described the 80/20 rule, where a small proportion of the population accounts for a large proportion of the total.

**Why Each Wrong Option is Incorrect**
**Option A:** is incorrect because it does not accurately describe the age and sex structure of a population.

**Option B:** is incorrect because it is a type of chart used to display the distribution of categorical data, but it is not specifically designed to display age and sex demographics.

**Option C:** is incorrect because it is a statistical measure used to describe the variability in a dataset, but it does not provide information about the age and sex structure of a population.

**Clinical Pearl / High-Yield Fact**
One important application of Pareto charts is in identifying areas of high risk for certain diseases, such as cardiovascular disease, which tends to affect older adults more frequently.

**Correct Answer:** C.