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Salem’s Secrets: A Case Study on Hypothesis Testing an… - National Center for Case Study Teaching in Science

Thursday12/11/08 Thursday Dec/11/08 11:53 AM

CASE TEACHING NOTES for

“Salem’s Secrets: A Case Study on Hypothesis Testing and Data Analysis” by Susan M. Nava-Whitehead, Sciences and Education Department, Becker College, Worcester, MA Joan-Beth Gow, Biology Department, Anna Maria College, Paxton, MA

I NTRODUCTION / B ACKGROUND This case study examines the Salem witch trials that took place in Salem, Massachusetts, in the late 1600s. It is designed to provide students with an opportunity to analyze and critique data and to help them understand the scientific method. We have used the case in a non-majors general biology course to teach students who have had little previous exposure to science and the scientific method. The use of this case study has led to increased comprehension and retention among these non-science majors, as evidenced by students’ selfselection of this topic when given essay options on examinations. Many aspects of the case could be amplified and emphasized for a variety of courses in addition to general biology. For example, the topic of mass hysteria could easily be expanded and integrated into a psychology or sociology course. The subject of mycotoxins in general, and ergot toxicity specifically, could be emphasized in a microbiology course. The aspect of mass psychogenic illness could be highlighted in epidemiology courses. Indeed, this is a perfect case study to use for interdisciplinary teaching. With regard to epidemiology, for example, Boss (1997) highlights how few students of public health are trained to consider mass hysteria as a differential diagnosis to explain an outbreak. In addition, a popular author has written a novel, Acceptable Risk, incorporating the events at Salem and fungal poisoning (Cook, 1994). The novel could be used to incorporate the case study into a freshman seminar class where aspects from a piece of literature are threaded throughout the course. The case also could be a perfect partner for a course in American history.

Objectives At the conclusion of this case, the student will: Apply the principles of the scientific method to analyze and evaluate evidence critically. Define the term “evidence” using scientific terminology: observable, measurable, repeatable. Outline the defining social dynamics of mass hysteria. Identify the signs and symptoms of ergot poisoning. Synthesize data to formulate and defend a conclusion. Appreciate and communicate that scientific understanding is contextual—it is interpreted at the technological level and within cultural norms of the time. In addition, enrichment opportunities exist for: http://www.sciencecases.org/salem_secrets/notes.asp

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Salem’s Secrets: A Case Study on Hypothesis Testing an… - National Center for Case Study Teaching in Science

Thursday12/11/08 Thursday Dec/11/08 11:53 AM

Cross-curriculum exploration (history of New England in 1692). An examination of ecology (environmental influence). Defining organizational schemata (fungus). Identifying biological toxins (in particular mycotoxins). Investigating biochemical effects of ergot on the central nervous system. Discussing the role of nutrition, age, and gender in susceptibility to toxins. Examining food sanitation and the history of food poisoning.

C LASSROOM M ANAGEMENT We have taught the case using an interrupted case study method in which students receive the case in parts, or sections, which they must complete in turn. The case is devised to take a single 75-minute classroom period. We have found that 75 minutes is sufficient to cover all of the basic aspects of the case. If further exploration of specific concepts is to be undertaken, more time would be needed. In addition to the case, students also receive a data management sheet as a handout to help them keep track of the information they glean from the case. We have found that students like to complete case studies with a tangible product in hand, particularly if they are to be tested on the information. The data management sheet serves that purpose.

Part I—Salem’s Secrets Students are asked to read Part I of the case study in advance of the class in which it will be discussed. In class, students are put into small groups, handed a copy of the data management sheet, and given five minutes to read Part I. The instructor then facilitates a class discussion regarding the concept of scientifically acceptable evidence. After extracting from the students their ideas of what constitutes evidence and writing these ideas on the board, the instructor leads the students to conclude that scientific evidence must be subject to some form of validation. The gold standard for evidence obtained experimentally is, of course, data that are measurable, observable, and repeatable. For observational studies, particularly those done retrospectively, these criteria cannot always be met (see Blocks of Analysis for further discussion of this topic). Students in groups are then asked to formulate a hypothesis, based on what they have read so far, explaining the events at Salem. They then are asked to use their newly learned definition of evidence to list in the data management sheet all the pieces of data that support the hypothesis they developed.

Part II—Mass Hysteria As students list pieces of evidence from Part I on their data management sheet, the theme of mass hysteria will emerge. The instructor facilitates a brief discussion on the concept of mass hysteria and then distributes Part II which includes a table describing selected mass hysteria events throughout history. Many students equate mass hysteria with fakery. The instructor should emphasize that victims of mass hysteria really do experience a set of symptoms, although there is no identifiable organic cause. The purpose of the table in Part II is to highlight the occurrence of this phenomenon throughout history and its relevance to modern times. Specific references to the events included in the table are included in the References section. Students’ frame of reference is such that they often believe that the phenomenon occurred “back then to those people” because of the victims’ lack of intelligence. Draw their attention in particular to the recent case of mass hysteria on a college campus. Unless one of the students has previously heard of the purported connection of ergot poisoning to the Salem witch events, it is unlikely at this point that anyone will propose a biological explanation. The next step in the progressive disclosure is to expand their thinking and lead them to another possible explanation for the Salem http://www.sciencecases.org/salem_secrets/notes.asp

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events.

Part III—Ergot: A Toxic Fungus The instructor next hands out Part III of the case study, essentially an information sheet on ergot. After the students read this new information, the instructor asks them to list in column 2 of their data management sheet evidence that ergot could have been responsible for the events at Salem. We have found that asking students to re-examine data previously listed in light of new evidence and technology is useful as a prelude to the discussion on the societal frame of reference in Part V of the case. At the bottom of column 2 in the data management sheet, students are asked to write a hypothesis different from their first one to explain the Salem events. The students are polled to see how many believe mass hysteria caused the events in Salem, how many believe ergot caused the events in Salem, and how many believe there is an altogether different explanation. Students like to go off on tangential discussions here and it is important to assist them in staying on task. For example, students love the idea of discussing witches and the supernatural, which is clearly not the point of this case study. Likewise, students will desire to “blend” hypotheses to include many parameters; the instructor should force the students to select a single explanation. At this point, students are wrangling with the two conflicting hypotheses they likely have developed. Both seem viable, based on observations they have made. It is appropriate now to expose students to some retrospective, quantitative data gleaned from information published during the Salem witch trials.

Part IV—Data Interpretation The instructor now shares with students how different scientists publishing in the well-respected journal Science, after examining the same data presented in the case, disagree in terms of the conclusions they drew from it. Linnda R. Caporael has argued that “the evidence suggests that convulsive ergotism, a disorder resulting from the ingestion of grain contaminated with ergot, may have initiated the witchcraft delusion” (Caporael, 1976). Nicholas P. Spanos and his collaborator Jack Gottlieb have argued to the contrary: “records of the events of 1692 do not support the hypothesis that ergot poisoning was involved” (Spanos and Gottlieb, 1976). Part IV of the case study presents a table from this second paper. The instructor should ask the students if they can find any patterns to the data. The instructor explains how the data are represented in a binomial table, examining whether or not certain symptoms were experienced by affected persons other than the initial group of girls. These data are important as they show that the signs and symptoms of being bewitched extended further than the initial 11 girls. The fact that others had the same symptoms could be evidence in support of either mass hysteria or ergot poisoning, depending on the interpretation. It should be noted that there are testimonies from witnesses (see Boyer and Nissenbaum, 1977) stating that the fits suffered by those “bewitched” were so intense that they could not possibly have been faked. Again, this could be support for either mass hysteria or poisoning. Victims of mass psychogenic illness do not feign illness. The symptoms they have are very real; there is just not an organic cause. Students are asked to use the data interpretation section of their data management sheet to incorporate information to make a defensible argument for either mass hysteria or ergot toxicity. At this point, the instructor should circulate in the classroom playing devil’s advocate, challenging the students’ ideas at this point. This section of the case in particular provides an excellent opportunity for team teaching—additional data from the disciplines of history and environmental science provide a more complete consideration of the cultural and environmental conditions of the time; some prompts are provided in the “Table Comparing Two Explanations for the Events at Salem,” which can be found in the password-protected http://www.sciencecases.org/salem_secrets/notes.asp

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answer key to this case (see Answer Key, below). This table can be handed out after students have been given a chance to make their own arguments, or the instructor can simply use it as his/her own guide. Once groups have had adequate time to work, they should share their position with the class, with a survey taken of the various groups’ positions. The instructor should facilitate a final discussion by intimating that majority rules; if a majority of the class selected and defended ergot toxicity, surely that must be the answer? Expect a lively discussion to follow. The instructor should end this section by asking students to decide as a group what they believed happened in Salem based on the evidence they have gathered and heard. As this question has not been answered in the literature, clearly students will not be able to answer it definitively either. Thus, the case is left open-ended. Instructors may choose to end the case study here or continue on to Parts V and VI.

Parts V— The Societal Frame: What is the Secret of Salem? and VI—Wrap up: The Societal Frame and Classroom Extensions Here the instructor should emphasize the iteration of the scientific method. It is also appropriate here to be sure students understand the distinction in science between hypotheses, theories, and laws. It should be emphasized to students that science builds on knowledge. As more data are accumulated and examined by more scientists who examine and interpret it in different ways, old hypotheses are discarded and new ones formulated. New technologies make it possible to examine old data in different ways. For example, if someone were to show symptoms of ergot poisoning today, a definitive urine test is available as a diagnostic tool. This is an opportune time to ask students what methods scientists employ today and what are the limitations of analysis. This discussion is outlined in the Scientific Method section in Blocks of Analysis below. At the end of the class, follow-up questions are distributed that expand on various aspects of the case that are relevant to the 21st century. These questions can be considered in class without any advance preparation on the part of students, or the instructor may choose to have students research and develop them further in a writing assignment; again, here is an opportunity for a cross-discipline assignment. The case study is left unresolved and, to our great pleasure, the study discussion does not end in the classroom Students often leave class conversing with each other about various aspects of the case and are clearly interested in pursuing it further. We are fortunate to have an on-line forum that provides a space for students to continue their classroom discussion.

B LOCKS

OF

A NALYSIS

The following are sections containing more detailed information of various aspects of the case that the instructor may choose to emphasize.

Scientific Method Often students are introduced to the scientific method as a series of steps to memorize. This does little to help them understand the actual process that scientists use to do science. Students also fail to understand that although not overtly stated, the scientific method is the litmus test used by the scientific community for publication and acceptance of the results of scientific research. In addition, while students can often grasp an experimental approach to science, they may have a harder time understanding that retrospective analysis of data also involves the scientific method. This case study gives them a slightly different approach to the http://www.sciencecases.org/salem_secrets/notes.asp

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scientific method than they may be used to. In the end, students come to the conclusion that evidence is available to support both hypotheses. Scientists published in the prominent journal Science do not agree based on their examination of the same data. This exemplifies one aspect of the scientific method students often miss. Hypotheses can never be proven true; they can only be proven false. In a retrospective study such as the cause of the events at Salem, data are collected and examined by many different scientists. If sufficient evidence is available to support a hypothesis, it becomes a theory. If evidence refutes a hypothesis, the hypothesis is discarded and a new working hypothesis is established. Typically in these types of studies, as new technology becomes available, old data are examined in new ways (see discussion on The Societal Frame below). The Theory of Evolution is an excellent example to use here. This theory was initially supported by data such as geographical and fossil evidence and has been further supported with molecular evidence as new technologies have become available. In conclusion, science is an iterative process of collecting and analyzing new data, as well as re-analyzing old data. Scientists do not always agree on how to interpret these data and this truly is the essence of science.

Mass Hysteria Collective human behaviors can range from innocuous crazes and fads to mass hysteria, delusions, and mass psychogenic illness. Documented cases of collective human behavior appear throughout history, and it is likely there are far more cases than are reported in the literature. A variety of cases of mass hysteria are described in Part II of the case, and many more can be found in the references cited. Boss (1997) is an excellent review. The common thread that ties these examples together is the rapid diffusion of embellished or sometimes completely erroneous ideas within a population. Often the population affected is a small, tight knit group in an enclosed setting, such as a school. Not all cases involve symptoms of illness, and examples range from the bizarre case in China in the early 1900s in which several students were convinced their penises were shrinking (Bartholomew and Sirois, 1996) to the mass hysterical dancing of thousands across Europe off and on for 500 years (Donaldson et al., 1997). Interestingly, ergot poisoning has been suggested as a possible cause of this dancing plague, also called St. Vitus’ Dance. Lest the students believe mass hysteria does not happen today, Bartholomew and Sirois (1996) provide a review of epidemic hysteria in schools and Engs et al. (1996) describe a recent case study of mass psychogenic illness in a large Midwestern state university. Students may find this college event particularly relevant. The symptoms demonstrated in Salem have been attributed to mass psychogenic illness, i.e., the swift spread of a set of symptoms for which there is no tangible explanation. Typically, the myriad of symptoms experienced by people involved in these outbreaks is not imagined; however, the symptoms cannot be attributed to an actual physical cause. Instead, apprehension and the belief of having been exposed to something harmful triggers the symptoms. Ask students to consider how they feel when they hear or observe someone else vomiting. Mass psychogenic illness is simply this response taken to an extreme. Interestingly, symptoms such as convulsions, abnormal movements, false beliefs, and spasmodic laughing were far more common in mass hysteria events a century ago than they are in more recent mass hysteria events (Boss, 1997). When many people become ill at the same time, physical exams and tests are normal, and if no environmental cause is detected, mass psychogenic illness may be at fault. In Salem, many people showed the same symptoms within the same time period. This could easily be attributed to mass hysteria. However, because the events occurred so long ago, no physical tests were done and it is impossible retrospectively to determine if an environmental toxin such as ergot was present.

Ergot and Other Mycotoxins http://www.sciencecases.org/salem_secrets/notes.asp

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Mycotoxins are poisons generated by fungi. They are secondary metabolites that have no known function for the fungus and are produced on many crops such as cereals, nuts, soybeans, and even fruit. Illness and sometimes death are caused by ingesting contaminated food. Reports of these events have occurred since the beginning of agriculture and possible references to ergotism exist as far back as 600 B.C.E. in Assyria (vanDongen and deGroot, 1995) and as recently as 1978 in Ethiopia (Demeke, Kidane, and Wuhib, 1979). It is useful for students to realize that ergotism exists in two forms, convulsive and gangrenous. Symptoms of both fo...