Therac-25 Analysis

This case exercise asks students to analyze a complex, real-world, fatal case, with special attention to three aspects: participant roles, ethical decision-making without the confounding of pragmatic (i.e., self-interest, non-ethical) factors, and consideration of preventative activities (what could have been done in advance to avoid the problem).

1. Learn Therac-25, an important case study, and realize that errors and bad decisions can injure and kill.
2. Practice analysis of ethical decision-making (and by extension become better ethical decision makers).
3. Detect and eliminate self-interest factors and other peripheral considerations when making an ethical decision.

1. Knowledge. Each person on a large project may see only the tip of the iceberg when there is a problem, making complete reporting more important (i.e., they alone cannot evaluate the severity of the potential problem). Huge problems can result from a concatenation of (apparently) insignificant details and annoyances. Injury and death are very real possibilities from software and other errors.
2. Skills. Complex case analysis; application of code-of-ethics planks to specific situations.
3. Attitudes. Ethical decisions (so called) should not be based on self-interest or other non-ethics considerations; a code of ethics is useful as a resource for decision-making; you should begin thinking about ethics and consequences at the beginning of a project, not after a disaster. 

1. Preparation (2 hours - homework - individual). Students thoroughly read the Leveson and Turner article, "An Investigation of the Therac-25 Accidents" ([IEEE] Computer, Vol. 26, No. 7, July 1993, pp. 18-41) outside class. On a second reading, they fill out Worksheet One - Participant List (as an electronic file, for later copies), which is a complete list of participants, both individuals and organizations, plus any questions or problems with their understanding of the case.
2. Analysis (1 class period - lecture plus small group). The analysis starts by reviewing the case, to ensure students follow the intricacies and people. Then they focus on one particular person or organization in detail.

1. Case review (20-30 minutes - in class - lecture or directed discussion). Collect a copy of Worksheet one in class (students should keep a copy for the ensuing discussion); outline/discuss the case, answering any questions students have (from Worksheet One); develop a master list of participants.
2. Participant analysis (20-30 minutes - in class - student pairs). Divide the class into pairs of students. Assign each pair one individual (or group of individuals) or one organization, from the master list of participants (one participant may be assigned to multiple groups). Pairs fill out and hand in a copy of Worksheet 2 (Participant Analysis).

1. To complete this case study there are three choices: a mock trial, in which students all provide questions and answers regarding each participant's ethics; or, presentations from each student pair about their participant's role; or, a short paper from each student summarizing the role of their participant. In each case, Worksheet 3 has questions which can be used as starting points for the discussions.

1. Mock Trial (1 class period - all students participate). Create a quasi-courtroom setting for a review board which is charged with investigating the Therac-25 case. Select a volunteer investigator (questioner), but tell the audience they are also required to contribute additional questions or corrections; change the investigator from time to time. Each participant will testify, which means that all students who studied that participant (at least one pair and maybe another pair) will be up front at one time, and give consensus answers. The investigator is charged with finding out what that participant knew, what they did, and what, upon later reflection, they think they should have done differently (or not done).
2. Presentations (1 class period, alternative to mock trial). Have student pairs exchange participant sheets (perhaps swapping individuals and organizations, so students see both categories). Each pair now familiarizes themselves with this new participant, and prepares a 5-minute summary for presentation covering what the participant did, didn't do, should have done, and why. Allow 1 or 2 audience questions after each presentation.
3. Papers (homework - alternative to mock trial). Exchange participant lists as for presentations. Then, each individual student writes a 1-page summary of this new participant, as outlined for presentations.

1. Wrap-up (optional - 30 minutes - in class). You may want to lead a final discussion, time permitting, that evaluates which decisions and actions were ethical, and which were unethical due to self-interest or other peripheral considerations. In addition, you may look at other aspects of ethical decision-making, such as the fact that most participants could not see the whole picture; that organizations are just a collection of individuals making decisions in the name of the group; whether any changed decisions, or set of changes, were likely to have changed the outcomes; and that individuals can anticipate that conflicts may occur which pit personal considerations against taking an ethical stand (e.g., you may lose your job if you report a problem), but they can prepare to some degree (e.g., stockpile six months salary just in case).

Worksheet One - Participant List: handed in and reasonably complete; this is a check for reading the article, as well as preparing for the first pair exercise.

Worksheet Two - Participant Analysis: pair grade for 2 students; thorough, thoughtful analysis of all the questions, handed in on time;

Mock Trial: participation grade, with demonstrated knowledge of the participant assigned;

Presentations and Papers: knowledge of (new) participant details, organized summary;

Students are asked to infer the thought processes of the participants, and should not be overly concerned as to whether they have discerned the actual, exact thinking behind the actions (or non-actions); any reasonable set of rationales will produce a good starting point for analysis and discussion. Students may legitimately argue that some participant simply did not think at all, so any "decision" was simply a default action. They will still be able to examine the reasons why that person did not actively think about the problem, and what they should have done.

Possible problems: Failure to thoroughly read and digest the article. Student (or pair) fails to complete one phase in time for the next phase. Non-participating students during trial ("testifying" or as audience members).

Many thanks to those in the summer 1999 workshop for suggestions and ideas, especially Jan Lee and Andrea Lawrence who helped develop the mock trial idea!

Dr. Judith S. Gurka, gurka@mscd.edu, Math/CS Dept., Metropolitan State College of Denver, Campus Box 38, PO Box 173362, Denver, CO 80217-3362

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