Natality

• "Natality," or birthrate, is defined as the number of children born in any given period of time. It is the number of live births per 1,000 people per year. Naturally, the amount of live births of any particular country is determined by several factors, such as nutrition, fertility, attitudes toward abortion, labor value of children, availability of contraception and culture. In countries such as the United States, the birthrate is decreasing. Many young couples are deciding not to have children for various reasons. However, in countries where contraception methods may not be readily available, or where there is much ignorance about such methods, the birthrate either increases or remains the same each year.
  
  

Mortality

• "Mortality" is the death rate of any country. It is defined as the number of deaths per 1,000 people in a year. Just like natality, mortality is dependent on many factors, such as disease, war, medical technology, availability of health care and nutrition.
  
  

Immigration

• The number of people moving into a country plays a huge role in the increase or decrease of a population. Immigration is mainly determined by the country's "pull" factor. In other words, how attractive is that country to different people? For example, the United States has a great deal of pull factors (jobs, availability of food, high-quality medical care) that attract many, despite the various immigration deterrents that people may encounter.
  
  

Emigration

• Opposite of immigration, "emigration" is defined as the number of people leaving the country. In this case, "push" factors (reasons for people to leave) play a main role in the number of people who emigrate each year. For example, in countries where famine, natural disasters or life-threatening discrimination are abundant, the emigration rate may be higher than in countries where a resident can find relative peace.