Exercise 3 showed that when age-specific fertility and mortality functions remain constant, a population ultimately reaches a stable age distribution, in which the proportion of individuals in each age class does not change with time (even though the overall size of the population may be changing). In this exercise we focus on the following question: How is the shape of the stable age distribution related to a populationís age-specific fertility and mortality rates; in particular, how is it related to the rate of growth of the population? 1. Before you start experimenting, give the above questions some thought, make a hypothesis, and explain your reasoning:
To do this exercise using Demography, open the problem file called "Exercise 4". Notice that you now see five windows. You will need to look at most of the available windows at various stages in this exercise, so you will have to get used to moving windows around on your screen so that you can see the one that you want. The four most important are Mortality vs. Age, Fertility vs. Age, Summary Statistics and one window that we have not yet used, Stable Age Distribution. In this exercise, since you will be making comparisons of populations with different mortality and fertility curves, Demography's marking feature may be useful. Marks allow you to save the state of the population at any time, then later come back to that state. For example, you can run a simulation for 100 time units, set a mark, then reset the model, change the fertility or mortality curves or the initial age distribution, again run the simulation for 100 years, and set another mark. You can then choose the Go to... command from the Marks menu to go back and forth between those two sets of windows and compare their values. To set a mark, delete a mark, or go to a mark, choose the appropriate command from the Marks menu. 2. Design an experiment (or experiments) that could test your hypothesis. Describe your design below. Please keep in mind that for your experiment to be useful in evaluating your hypothesis, you should try to change only one thing at a time. If you want suggestions, here are some hints, but you should feel free to describe your experiment and then go ahead and do it.
3. Describe your results.
4. What conclusions can you draw from this experiment? Is it consistent with your initial hypothesis? If not, can you explain why. Can you suggest other experiments that could be done to help answer the original question?
5. What are the some of the implications of your findings for the human population?
IMPORTANT: Before you proceed to the next exercise, make sure that you have talked to one of your instructors about your experiment and your results!