**Core Concept**
The APGAR score is a simple, widely used assessment tool to evaluate the health and well-being of newborn infants. It is a quick, five-point score that assesses five components: heart rate, respiratory effort, muscle tone, reflex response, and skin color. The APGAR score is usually performed at one and five minutes after birth.

**Why the Correct Answer is Right**
The APGAR score does not include respiratory rate. Instead, it assesses respiratory effort, which is an essential component of the score. Respiratory effort is evaluated by observing the newborn's breathing pattern, including the depth and rate of breathing, and whether the infant is making any attempt to breathe. The respiratory effort component is crucial in determining the infant's overall health and need for immediate medical attention. The correct assessment of respiratory effort can help identify potential respiratory distress or other complications.

**Why Each Wrong Option is Incorrect**
**Option A:** Respiratory effort is a component of the APGAR score, not respiratory effort's specific measurement (like rate).
**Option B:** Heart rate is indeed a component of the APGAR score, making it a correct answer and not a distractor.
**Option D:** Colour is also a component of the APGAR score, making it a correct answer and not a distractor.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the APGAR score is a quick, initial assessment tool and not a definitive measure of a newborn's health. A low APGAR score does not necessarily indicate a serious problem, and a high score does not guarantee perfect health. The APGAR score should be used in conjunction with other assessments and clinical evaluations to determine the overall health and well-being of the newborn.

**✓ Correct Answer: C. Respiratory rate**