In the late 1960s and early 1970s, marriage and fertility rates dropped as the Baby Boom generation came to an end. The primary reason why the birth rate declined in the United States in this time period was the relative liberation of women in American society. Women gained greater access to higher educational and were given more opportunities in the work place. Additionally, contraception became available and widely used for the first time. As a general rule, where education of women is high and contraception is easily available, fertility rates will be low.

Crude birth rate indicates the number of live births occurring during a year per every 1,000 people in a given population in a given year.

The “natural increase rate” is a statistic used to measure the growth of population in a region, exclusive of immigration and emigration. It only considers the crude birth rate and the crude death rate. If the death rate is higher than the birth rate, then the region has a “negative natural increase rate.”

The “Green Revolution” is the name given to a series of technological innovations in the 1940s, 50s, and early 60s that led to a massive growth in agricultural production around the world in the late 1960s. This led to massive population growth, particularly in the developing world.

Italy, like many Western European countries, is currently experiencing a negative natural increase rate (which means the population is falling). The United States of America continues to experience population growth, although a lot of it is driven by immigration. Brazil and Mongolia, you might infer, have modest levels of natural increase. But, Angola is in Sub-Saharan Africa and represents the most likely correct answer for this question.

The "baby boom" generation began in 1946, the year after the end of the Second World War, and lasted until 1964. This generation is primarily unique to the United States, although other Western countries experienced a similar spike in birth rate and lowering of the death rate. The baby boom generation began when the millions of soldiers returned home from war and were offered unprecedented job opportunities and access to higher education. Marriage rates and fertility rates both rose as the population skyrocketed.

You can use an age distribution to approximate survival rates by calculating the difference proportion of individuals in age classes.

Total fertility rate measures the number of children conceived by the average woman over the course of her lifetime. The total fertility rate of most of the developed world is around, or slightly less than, two, whereas in much of Africa, the total fertility rate is in excess of four. Other than Sub-Saharan Africa, which has the highest total fertility rate, most of the world’s countries with total fertility rate in excess of four can be found in the Middle East, stretching from Jordan in the West to Pakistan in the East.

Improved healthcare can have conflicting and widely variable influences on the rate of population growth. It rather depends on the starting point from which you are improving. For example, in South Sudan, increased access to medicine and better prenatal care would lead to a rapid growth in population in a short space of time; however, in Germany, improved healthcare would provide contraception and family planning advice, which would lead to a declining rate of population growth.

The period from 1964 to around 1980 is often called the “Baby Bust.” This is because the total fertility rate declined significantly from the era of the “Baby Boom” generation. The total fertility rate declined for many different reasons, but the primary reason was the relatively dramatic increase in female empowerment during this time period. More women were university-educated, more were entering the workforce, more were using contraception, and more were waiting longer to have children. The cumulative effect was a decline in the natural increase rate and the total fertility rate.