Bell Work Demographers study POPULATION Make a prediction: What certain attributes “characteristics” of a society might demographers focus on?

Understanding Demography Objective: Explain the key terms of demography. Analyze population pyramids.

The Study of Population Every country goes through a change in its population structure as it develops – this is called the demographic transition Important terms to understand: More Developed Country (MDC) or Developed Less Developed Country (LDC) or Developing

What do demographers look at in a country? Crude Birth Rate (CBR) - # of people born every year per 1000 people What factors do you think affect CBR? Wealth, medical advances, opportunities for women, low infant/child mortality rates, availability of contraceptives Crude Death Rate (CDR) - # of deaths every year per 1000 people What factors do you think affect CDR? Better/more stable access to food, access to medicine, composition of population (lots of old people?), epidemics, famine, sanitation facilities

CBR and CDR determine the… Natural Increase Rate (NIR) – percentage by which a population grows in a year The difference between CBR and CDR CBR minus CDR Sometimes called natural change NIR affects the Doubling Time # of years it takes to double the present population at current growth rates

Doubling Time Riddles A father complained that his son’s allowance of $5 per week was too much. The son replied, “OK Dad. How about this? You give me a penny for the first day of the month, 2 cents for the second, 4 cents of the next, 8 cents of the next and so on for every day of the month.” His father readily consented Who was more clever? What would the son’s allowance be on day 31? What would his allowance for the month be? Do you know how long it will currently take for the world’s population to double?

Another riddle Doubling time is the time it takes a population to double at a constant rate of growth. Bacteria, for instance, multiply by division. One bacterium becomes two. Then two divide into four; the four divide into eight, and so on. For a certain strain of bacteria, the time for this division process is one minute. If you put one of these bacterium in a bottle at 11pm, the entire bottle will be full by midnight. When would the bottle be half full? How do you know? Suppose you could be a bacterium in this bottle. At what time would you first realize that you were running our of space?

Demographers also study… Total Fertility Rate (TFR) – the average # of children a woman will have throughout her childbearing years When a country has a TFR at or less than 2.1, the population is not growing – only maintaining itself – because couples are only having enough children to replace themselves The magic number 2.1 is called the Replacement Rate 2.1 TFR/Replacement Rate results in… Zero Population Growth (ZPG) – same # are born and die in a year, CBR=CDR

Population Pyramids A visual representation of age and gender cohorts (groups) within a country MDC’s and LDC’s will have different looking population pyramids because they have different population structures Shape of the pyramid is determined by the CBR in each country Pyramid shows the percentage of the total population in 5- 10 year age groups Males shown on the left, females on the right Now, we’re going to practice drawing population pyramids!!