פרופ' יובל שחר הנדסת מערכות מידע

Information Systems Engineering Prof. Yuval Shahar, M.D., Ph.D.

תרגיל 4

ניתוח וקבלת החלטות במערכות מידע

Judgment and Decision Making in Information Systems

  1. Read Chapter 3 by Owens and Sox, in the Shortliffe et al. 2000 Medical Informatics textbook. Answer questions 1, 2, 3, 4, 6, and 10.
  1. Consider de Dombal’s system [Leaper et al., BMJ 1972] for diagnosis of acute abdominal pain.
  2. What might be involved in using the system, say, in Bombay, India? What, in your opinion, might be the effort needed? Explain.
  3. Should it be the ideal of the system to reach a 0% unnecessary laparotomy rate for cases in which appendicitis is suspected, that is, a 100% positive predictive value, which means no false positives in which the patient’s abdomen was explored surgically unnecessarily? Why or why not?

Read Owens et al., MDM, 1997, and Nease and Owens, MDM, 1997 and answer the following questions.

  1. Prenatal testing for developmental defects such as Down's syndrome (DS) is widely available. A common test during the second trimester of pregnancy is amniocentesis (AC), whereby amniotic fluid is aspirated from the womb for chromosomal analysis and biochemical testing; another one is high-resolution ultrasound (HRUS). Unfortunately, both tests are costly, and AC carries a significant risk of inducing miscarriages and losing the baby. DS is not the only defect diagnosable through AC; for instance, a higher-than-normal measurement of alpha-fetoprotein (AFP) in the amniotic fluid provides evidence for the possibility of open-neural–tube defect (ONTD). However, ONTD can be detected early in the second trimester (with lower sensitivity and specificity) by the HRUS test. Furthermore, the parents’ individual preferences, regarding termination of pregnancy versus the risk of life-long disability for the baby for each of the diseases, as well as local variability in procedure risks (risk of spontaneous miscarriage after AC), are crucial for the decision.
  2. Draw an influence diagram (just labeled nodes and arcs) that describes the above decision. The decisions include whether to perform AC, HRUS, or TERMINATION; diseases include DS and ONTD. Tests include AC, HRUS, AFP, Chromosomal Analysis CA). Assume that AFP and CA will always be done after AC, but, like all tests and procedures, have a cost. Include a deterministic node for monetary values and a value node for the overall values of the outcome. Ignore labor and miscarriage costs.
  3. Show how the diagram changes if we add that (1) AFP and CA are tests also need a decision, following AC, and (2) there is a procedure, Chorionic Villous Sampling (CVS), that can tell us in the first trimester whether the baby has DS, but is costly and has a higher risk of miscarriage due to the procedure.
  4. Assuming each decision has two alternatives and each uncertainty has just two degrees of distinction, how many outcome possibilities are needed to fully characterize the full AC decision problem with a decision tree? Explain.
  1. Paz Co., a leader in petroleum products, is considering a move into the cellular phone market. The idea is to persuade their regular customers to get cheap phones when they buy gas at the Paz gas stations. The phones will have new utilities such as a global positioning system chip that will help the customers on the road. You are the senior strategic consultant of this new project. There are multiple uncertainties, such as: How many customers still are available for the cellular market, what is the probability that those available will actually agree to buy a new type of phone, how much they will use the phones (airtime), how much competition will exist at the time the phones go to market (which will affect the number of phones sold and the price and profit margin for each phone), whether to invest in an R&D department just for phones or hire an outside consulting company for that, and whether to pay a market research company that is considered to have good but not perfect estimates of the potential market.
  2. Draw an influence diagram (just labeled nodes and arcs) that characterizes the Paz decision. Try to include the factors mentioned above and other decisions and chance and deterministic nodes you consider relevant (e.g., political and economic situation, etc).
  3. Try to estimate which uncertainties are most important in your diagram. Explain qualitatively why you think so.
  4. Simplify the diagram to enable making the following calculation: Fill in all probability (for the chance nodes) and utility values (for the $ outcomes) in your model (use reasonable estimates for each of the hidden probability and value tables). Using either a decision tree or an influence diagram technique, solve the diagram to find the optimal decision for the nominal (default) values. Create a tornado diagram for the chance variables, showing the ranges of the expected utility of the overall decision, when each variable changes and the rest stay in the nominal value.
  5. Given your numbers, what is the value of information in your case for using the marketing company?
  6. Assuming each decision has two alternatives and each uncertainty has just two degrees of distinction, how many outcome possibilities are needed to characterize your original (full) Paz problem with a decision tree? Explain.