# Health Informatics Assignment Week 3

## Questions for Discussion

1. Calculate the following probabilities for a patient about to undergo CABG surgery (see Example 2):
1. The only possible, mutually exclusive outcomes of surgery are death, relief ofsymptoms (angina and dyspnea), and continuation of symptoms. The probability of death is 0.02, and the probability of relief of symptoms is 0.80. What is the probability that the patient will continue to have symptoms?
2. Two known complications of heart surgery are stroke and heart attack, with prob-abilities of 0.02 and 0.05, respectively. The patient asks what chance he or she has of having both Assume that the complications are conditionally independent, and calculate your answer.
3. The patient wants to know the probability that he or she will have a stroke giventhat he or she has a heart attack as a complication of the surgery. Assume that 1 in 500 patients has both complications, that the probability of heart attack is 0.05, and that the events are independent. Calculate your answer.
2. The results of a hypothetical study to measure test performance of the PCR test forHIV (see Example 1) are shown in the 2 × 2 table in Table 3.9.
1. Calculate the sensitivity, specificity, disease prevalence, PV+, and PV.
2. Use the TPR and TNR calculated in part (a) to fill in the 2 × 2 table in Table 3.10. Calculate the disease prevalence, PV+, and PV.
3. You are asked to interpret a PCR HIV test in an asymptomatic man whose test waspositive when he volunteered to donate blood. After taking his history, you learn that he is an intravenous-drug user. You know that the overall prevalence of HIV infection in your community is 1 in 500 and that the prevalence in intravenous-drug users is 20 times as high as in the community at large.
1. Estimate the pretest probability that this man is infected with HIV.
2. The man tells you that two people with whom he shared needles subsequently diedof AIDS. Which heuristic will be useful in making a subjective adjustment to the pretest probability in part (a)?

Table 3.9. A 2 × 2 contingency table for the hypothetical study in problem 2.

 PCR test result Gold standard test positive Gold standard test negative Total Positive PCR 48 8 56 Negative PCR 2 47 49 Total 50 55 105 PCR = polymerase chain reaction. Table 3.10. A 2 × 2 co ntingency table to complete for p roblem 2b. PCR test result Gold standard test positive Gold standard test negative Total Positive PCR x x x Negative PCR 100 99,900 x Total x x x

PCR = polymerase chain reaction.

3. Use the sensitivity and specificity that you worked out in 2(a) to calculate the post-test probability of the patient having HIV after a positive and negative test. Assume that the pretest probability is 0.10.
4. If you wanted to increase the post-test probability of disease given a positive testresult, would you change the TPR or TNR of the test?
4. You have a patient with cancer who has a choice between surgery or chemotherapy.If the patient chooses surgery, he or she has a 2 percent chance of dying from the operation (life expectancy = 0), a 50 percent chance of being cured (life expectancy = 15 years), and a 48 percent chance of not being cured (life expectancy = 1 year). If the patient chooses chemotherapy, he or she has a 5 percent chance of death (life expectancy = 0), a 65 percent chance of cure (life expectancy = 15 years), and a 30 percent chance that the cancer will be slowed but not cured (life expectancy = 2 years). Create a decision tree. Calculate the expected value of each option in terms of life expectancy.
5. You are concerned that a patient with a sore throat has a bacterial infection thatwould require antibiotic therapy (as opposed to a viral infection, for which no treatment is available). Your treatment threshold is 0.4, and based on the examination you estimate the probability of bacterial infection as 0.8. A test is available (TPR = 0.75, TNR = 0.85) that indicates the presence or absence of bacterial infection. Should you perform the test? Explain your reasoning. How would your analysis change if the test were extremely costly or involved a significant risk to the patient?
6. What are the three kinds of bias that can influence measurement of test performance?Explain what each one is, and state how you would adjust the post-test probability to compensate for each.
7. How could a computer system ease the task of performing a complex decision analysis? Look at the titles of Chapters 9 through 18 of this text. What role could each kind of system play in the medical-decision process?

DSS's involve programs focused on information. A properly constructed DSS is an immersive software-based system designed to help decision-makers publish helpful info from either a mix of raw data, documents, and specific observations, or marketing strategies to resolve any issues and make informed decisions. Decision-making software (DM software) is data analytics technology that enables organizations and individuals start making decision and take judgements, usually by order to rank, optimizing or deciding from either a range of options. One of Computers' greatest drawbacks when decision-making tools includes their incapability to take into account ethical principles in decision-making. Apart from, computers make their own decisions based on human-collected data. Individuals were unable to work through their own. Computers are stronger decision-makers that humans, because the response is very fast and accurate, while decision-making by humans is clunky compared to machine decisions. Apart from, computers make their choices based on human-collected data. Artificial intelligence is described by the scientists as tools that can help to manage ability to problem. The author hopes to get all these technologies into supervised clinical use during the context, when there is an issue and a computer simulation which can solve it and facilitate decision taking in actual world. Computer systems boost the productivity, and the program operating on them would be well known. Health decision-making allows the practitioner to extend empirical experience to a particular subset with health information in order to make the decision it might be a prediction, a diagnosis, a method of action or the collection of more testing. It allows computers to make those choices in a manner quite human-like. Individual decision-making isn't really flawless and it can give various judgments even when the input is stated. Human decision-makers negotiate with choices, utility services, costs, benefits, aims and priorities when generating ethical decision-making. To characterize the question, all of those should be taken into consideration and the required and consequence decided. Some computer software also help one manage the thinking and enable them to carry out work more effectively.

8. When you search the medical literature to find probabilities for patients similar to oneyou are treating, what is the most important question to consider? How should you adjust probabilities in light of the answer to this question?

The very first phase includes making a trial showed about likelihood of a patient having a condition. Instinctively a practitioner creates a conviction about the possibility of illness following an assessment and physical examination. This decision might well be based on anecdotal evidence, or medical journal awareness. A doctor's assumption about possibility of illness is typically inherent; he or she could clarify it by providing a specific calculation of the possibility of illness. This approximate likelihood, rendered until enough knowledge is collected, is the likelihood of disease subsequent to it or pretest likelihood. The clinical evidence also includes information on the prevalence of diseases in a particular population. A insightful decision-maker would be extremely worried that the approximation might have been in inaccuracies, especially because it is often challenging to get the documentation necessary to create the approximation from the scientific journals. Healthcare providers occasionally demonstrate reservations about the assessment of decisions so because assessment may rely solely on probability distributions which must be approximated, such as the likelihood of pretesting. In such situations, abnormalities, particularly moderately unusual outcomes, can be difficult to decipher. Much farther observations into incidence of anomalies will help enhance the organizing of logical tests as well as the analysis of tests. The following calculations of the specimens and the stated action limits have been used to determine, separately, the amount of abnormalities and significantly irregular findings.

9. Why do you think physicians sometimes order tests even if the results will not affecttheir management of the patient? Do you think the reasons that you identify are valid? Are they valid in only certain situations? Explain your answers. See the January 1998 issue of Medical Decision Making for articles that discuss this question.
10. Explain the differences in three approaches to assessing patients’ preferences forhealth states: the standard gamble, the time trade-off, and the visual analog scale.
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