Why are population predictions important? Read the excerpted page from "Population Projections," an article from the February 2005 issue of Trends magazine, published by the Alaska Department of Labor and Workforce Development Research and Analysis section.

The model shown starts with the following statistics. You will be able to change the birth, death, immigration, and emigration rates, but the starting population is fixed. Download the Annual Components of Population Change and print it out. This page is also excerpted from the Feb. 2005 Trends article. You will need this information to help you complete this activity.

NOTE: Please do not change anything in the model until instructed. If you need to reset the model to its original values, reload the page in your browser.

1. What are the components of the model?

   Above is a model that you will use to predict the population of Alaska up to the year 2025. There are several components to the model.

   1. A "line graph" and "bar graph" selector. The default is a line graph. If you select the bar graph, single and double arrows will appear below the graph. You may then select specific years. If you select the double arrows, you can watch the population change throughout the entire range of years.

   2. A graph of the population prediction. The years from 2004 to 2029 are shown on the x-axis. The population of the population is shown on the y-axis. What color is the line of the graph?

   3. The 4 parameters of the model. What are the parameters of the model? These have "sliders" so you can change the values. The most precise way to change a parameter is to click into the parameter box and then type in your value. The graph will be immediately updated.

   4. Text Output button. Press the button now. You should get a two-column chart of the year and the size of the population. Exponential notation is used. For example, the first entry in the chart is 2000.0 6.55e5. This means that the starting population is 6.55 x 10⁵ = 6.55 x 100,000 = 655,000. Scroll down to the end of the chart. What is the predicted population in 2029?
      There are additional selectors in this area of the model, but you don't need to use them.

   5. Section concerned with the initial values, time step, and mathematical methods. You probably recognize the range of values for the x-axis, the year 2004 through the year 2029. The y-axis minimum and maximum values are also shown. The time step is also shown. the time step is 0.25, which means that the prediction is calculated every .25 year or ¼ year. You can also see this in the text output. You may close the text output if you have not done so yet. Finally, in the section is a selector for different methods by which the results may be calculated. The default value is a method called "Euler's" method. This is the least accurate but requires the least amount of computational power. For our purposes, the default Euler's method is accurate enough.

2. How Can the Model Be Used to Make Predictions?

   As you can see from the table at the top of this page, some of the data for this model comes from data obtained in 1998 through 2000. Compare this model with the data for 2003-2004 provided. (You were asked to print out the Annual Components of Population Change page.)

   1. How has the birth rate changed from 1998-1999 to 2003-2004?

   2. How has the mortality rate changed from 1998-1999 to 2003-2004?

   3. Look at the "Net Migrants" column in the chart. What does a positive number mean? What does a negative number mean? Have the changes in "Net Migrants" from 1998-1999 to 2003-2004 followed a pattern?

   4. Look at the graph below. It combines the births deaths into "Natural Increase" and combines the migrants into the state and migrants out of the state into "Net Migrants." Which factor is more predictable, "Natural Increase" or "Net Migrants?"
      

   5. Imagine the following scenario. A natural gas pipeline is going to be built in Alaska. The rate of immigration increases to 0.070 because of the resulting economic boom. The emigration rate declines to 0.050. In this scenario, the birth rate declines somewhat because the population is aging. For the same reason, the death rate will increase a little. Use the initial values of 0.015 for the birth rate and 0.005 for the death rate to complete this question. Predict the population of Alaska in 2029 using these new rates. It may be easier for you to type in your values than to use the slider. HINT: you will need to used the text output to get an accurate result.

   6. Why might this not be an accurate prediction?

Stella2Java © 1999-2001 The Shodor Education Foundation, Inc.