What does the fertility rate measure?

The fertility rate is an important demographic measure that specifically refers to the number of babies born per 1,000 women of childbearing age, typically defined as those aged between 15 and 49 years. This measure provides insight into a population's reproductive behavior and potential growth. A higher fertility rate indicates that more children are being born, which can influence population size, structure, and future trends.

In terms of context, measuring the total number of births in a year does not account for the size of the female population of childbearing age, which is crucial for understanding fertility dynamics. The number of individuals in a population is a broader measure that does not specifically relate to birth rates or reproduction. Additionally, the average lifespan of a population relates to mortality rates rather than fertility, indicating the age to which individuals typically live rather than how many children are being born. Thus, the correct understanding of fertility rate is that it quantifies reproductive output among women in the reproductive age group, making option C the accurate choice.