## Core Concept
Mortality rates between countries are best compared using a measure that accounts for the differences in age distributions of the populations being compared. This is because mortality rates can be influenced by the age structure of a population, with older populations typically having higher mortality rates.

## Why the Correct Answer is Right
The correct answer, **Standardized Mortality Ratio (SMR) or Age-Standardized Mortality Rate**, is a measure that adjusts for the age distribution of a population. This allows for a more accurate comparison of mortality rates between countries with different age structures. Age-standardization is performed using a standard population, which enables the calculation of what the mortality rate would be in each country if it had the same age distribution as the standard population.

## Why Each Wrong Option is Incorrect
- **Option A:** Crude Mortality Rate does not account for the age distribution of a population. It is a simple ratio of total deaths to total population, which can be misleading when comparing countries with significantly different age structures.
- **Option B:** Proportional Mortality Rate refers to the proportion of deaths in a population due to a specific cause. While useful for understanding the distribution of causes of death, it does not directly address the comparison of overall mortality rates between countries.
- **Option D:** Infant Mortality Rate is a specific measure that focuses only on deaths of infants under one year of age per 1000 live births. It is an important indicator of health status but does not provide a comprehensive comparison of mortality across all ages between countries.

## Clinical Pearl / High-Yield Fact
A key point to remember is that when comparing health statistics, such as mortality rates, between different populations, **age-standardization** is crucial. This process helps to ensure that the comparisons are not skewed by differences in the age distributions of the populations being studied. This concept is frequently tested in exams and is relevant for public health and epidemiological studies.

**Correct Answer: C. Age-standardized mortality rate.**