**Core Concept:**
The Human Development Index (HDI) is a composite index that measures the overall development of a nation based on three primary components: life expectancy at birth, educational attainment, and per capita income. These components are used to evaluate the overall well-being of a population.

**Why the Correct Answer is Right:**
The HDI is a composite index that combines three essential components: life expectancy at birth, educational attainment, and per capita income. By considering these factors, the HDI aims to evaluate the overall well-being of a population, reflecting the quality of life and standard of living.

**Why Each Wrong Option is Incorrect:**
A. Life expectancy at birth is a critical component of the HDI, as it reflects the overall health and longevity of a population.
B. Educational attainment is crucial as it determines the level of human capital and contributes to the development of a nation.
C. Per capita income is essential as it reflects the standard of living and purchasing power of a population.
D. All three components are essential in evaluating the overall development of a nation, making option D incorrect.

**Clinical Pearl / High-Yield Fact:**
Understanding the importance of HDI components is crucial for evaluating the overall well-being of a population and making informed decisions related to public health, education, and economic development.

**Correct Answer:** D. All three components are essential in evaluating the overall development of a nation, making option D incorrect.