## **Core Concept**
The dependency ratio is a measure used to indicate the ratio of people in the "dependent" ages (those who are either too young or too old to work) to those in the "working" ages. It is an important demographic measure that helps in understanding the economic burden on the working population. The denominator in the dependency ratio calculation represents the total working-age population.

## **Why the Correct Answer is Right**
The dependency ratio is calculated as the sum of the youth population (ages 0-14) and the elderly population (ages 65 and over) divided by the working-age population (ages 15-64), then multiplied by 100 to get a percentage. The working-age population, which is typically considered to be those aged 15-64, serves as the denominator. This is because these individuals are generally considered to be the productive segment of the population, capable of supporting themselves and potentially their dependents.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because the numerator of the dependency ratio consists of the youth (0-14 years) and elderly populations (65 years and above), not the denominator.
- **Option B:** This option suggests the total population as the denominator, which is incorrect because the dependency ratio specifically aims to compare the dependent populations to the working-age population, not the total population.
- **Option D:** This option refers to the population under 15, which is part of the numerator (the dependent population), not the denominator.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that a higher dependency ratio indicates a greater burden on the working population to support the dependents, which can have implications for social security, healthcare, and economic policies.

## **Correct Answer:** B. 15-64 years age group.