Model Description:

We are using STELLA to model the growth of the number of cases of AIDS in the United States. Included is a model of exponential growth and one which patterns the spread of the disease in the entire United States as well as an Excel Spreadsheet which contains data found at the following web site: <http://www.cdc.gov/hiv/stats/hasrlink.htm>. The data points were graphed on a TI83 graphing calculator and it was determined that the best fit was a logistic curve.

Activities and Procedures:

Students will study this model as part of their introduction to STELLA, go to the same web site to obtain numbers of AIDS cases in their assigned states from 1982 through 2001 and construct a STELLA model to reflect their numbers. They will first use graphing calculators to estimate the carrying capacity for their graph and experiment with different values for the growth factors until they are satisfied with their results.

References and Resources:

Good data is available at this web site: <http://www.cdc.gov/hiv/stats/hasrlink.htm>

Information on the AIDS epidemic is available at <http://www.unaids.org/wac/2000/wad00/files/WAD_epidemic_report.htm>

Teaching Strategies:

AIDS is a very real issue in our world. First we can really engage the students by having them do some research on the subject for themselves. If we look at the spread for the first 10 years, the growth appears to be exponential. When we include more recent data, the curve appears to be logistic. We can begin with the exponential model and then extend to the logistic one.