| There are three major factors that account for the | | | | the likelihood of nuclear power plant accidents. On the |
| difficulty the defense has with presenting a general | | | | other hand, people under-estimate high probability |
| causation case to a jury. They have to do with the | | | | hazards that are less memorable such as certain |
| ways in which people process information; the | | | | diseases (Covello, V.T. (1995) "Risk Comparison and |
| relevance of general causation evidence to what the | | | | Risk Communication: Issues and Problems in |
| jurors care about; and the complexity of the | | | | Comparing health and environmental Risks in |
| evidence. This article will discuss the first of these. | | | | Kasperson, R.E. and P.M. Stallen (eds), Communicating |
| In every day life people do not always think in the | | | | Risk to the Public, Dordecht: Kleuer Academic Press). |
| most logical and rational fashion. The work of two | | | | These points are very important in the context of a |
| different Nobel Prize winners is illuminating here. | | | | scientific defense of causation in the courtroom. If |
| Herbert Simon won the Nobel Prize for Economics in | | | | the plaintiff has suffered an injury that is familiar to |
| 1978. He developed a theory of decision-making | | | | the juror or easily imagined, then the juror is likely to |
| based on the idea of bounded rationality. People face | | | | overestimate the likelihood of it happening and |
| uncertainty about the future and there are costs | | | | believe the defense should have anticipated this |
| that are often insurmountable that are associated | | | | likelihood and done something to prevent it (further |
| with acquiring information in the present. | | | | reinforced by the hindsight bias in which people tend |
| Because of this, people are unable to make fully | | | | to view something that happened as inevitable and |
| rational decisions. They only have "bounded | | | | therefore something that could have been |
| rationality." People are either unable or unwilling to | | | | anticipated). If the injury or illness is unfamiliar to the |
| maximize the rationality of the decisions that they | | | | juror, the juror is likely to see it as a rare event that |
| make (because they are unable or unwilling to acquire | | | | therefore is likely to have an idiosyncratic cause (such |
| all the information they need to do so). They make | | | | as the product or substance the plaintiff claimed |
| decisions by "satisficing"; setting an aspiration level, | | | | caused it). |
| which, if achieved, they will be happy enough with | | | | The second heuristic is the representativeness |
| (Simon, Herbert (1997) Administrative Behavior 4th | | | | heuristic. This refers to the tendency of people to |
| Edition, New York: The Free Press). | | | | ignore the size of the sample and the base rate |
| Let's take as an example a decision about whether | | | | when making inferences about causation. Let us take |
| to fly or take the train from Boston to New York | | | | the example of PCBs. Here the literature used by |
| where time is of utmost importance. Attempting to | | | | plaintiffs is replete with scientific studies that rely on |
| make a maximally rational decision a person might | | | | very small sample sizes and which make no attempt |
| investigate the percentage of on-time arrivals for | | | | to compare the prevalence of a disease the sample |
| both the plane and the train; how this is affected by | | | | to the prevalence of the disease in the general |
| the time of day; and the impact of weather | | | | population. But these studies are still appealing to |
| conditions. However, what is more likely is that the | | | | jurors. If someone has PCBs in their blood and a |
| person will ask a few people who have taken both | | | | disease that has been related to PCB exposure, |
| modes of transportation about their experiences with | | | | jurors tend to ignore the base rate of the |
| on-time arrival. That information will be satisficing. | | | | percentage of people in the population with PCBs in |
| In the courtroom, the jurors are given enormous | | | | their blood (which is one hundred percent). |
| amounts of information in a very unnatural manner. | | | | The work of Paul Slovic on the perception of risk |
| What the defense lawyers and their expert | | | | also tells us a great deal about how laypeople's |
| witnesses often attempt to do is provide jurors with | | | | reasoning affects how they will see the defense's |
| the information they need to make a maximally | | | | evidence on general causation (for a good summary |
| rational decision. It would take a superhuman effort | | | | of his work, see Slovic, Paul and Elke U. Weber |
| to absorb, understand, and remember all this | | | | (2002), "Perception of Risk Posed by Extreme |
| information in the artificial format of the courtroom. | | | | Events," Paper prepared for discussion at the |
| This is particularly true in a complex toxic tort or | | | | conference "Risk Management Strategies in an |
| products liability case. Jurors make decisions based on | | | | uncertain world," Palisades, New York, April 12-13, |
| what they generally know to be an incomplete | | | | 2002.). Slovic points out that the way in which |
| understanding of the evidence. They seek to make | | | | experts calculate risk differs greatly from how |
| decisions that will be satificing to them, even if the | | | | laypeople calculate risk. In both instances there are |
| are not maximally rational. What we often find out | | | | subjective components. |
| from jurors when they have listened to all the | | | | Applying Slovic's findings to a toxic tort case, for |
| evidence on causation that what is determinative for | | | | example, a juror will be more likely to perceive a |
| them is the experience they, their family members, | | | | substance as possessing great health risks if, among |
| and friends may have had with the substance in | | | | other things, exposure to the substance was |
| question. | | | | involuntary, the plaintiff did not know he/she was |
| Some jurors also stop making the cognitive effort to | | | | exposed, the effect of exposure was delayed, and |
| acquire the information presented to them in the | | | | the risks and benefits to the public are unfairly |
| generally mistaken belief that a fellow juror is | | | | distributed. At one end of the spectrum is a situation |
| acquiring it for them (a satificing result). Instead of | | | | where a worker who had been warned of the |
| asking ourselves what a juror would want to know in | | | | dangers of exposure to a chemical used in |
| order to make a reasonable decision about the | | | | manufacturing an important product knowingly |
| relationship between exposure to a substance and a | | | | exposes himself to the chemical and suffers an |
| disease, we mistakenly ask ourselves what we want | | | | immediate injury. |
| to tell them. The consequence is that they get too | | | | At the other end of the spectrum is a person who |
| much information. Like all of us, jurors have a handy | | | | as a child was exposed through groundwater |
| ability to forget, reinterpret, and disbelieve | | | | contamination to the same chemical which was |
| information that is not consistent with the way they | | | | disposed of as waste and develops an injury many |
| have decided to process the information. | | | | years later. A juror's perception of the risk of the |
| The work of the 2002 Nobel Prize in Economics, | | | | chemical to the public at large (or to him or herself) |
| Daniel Kahneman (and his late colleague, Amos | | | | will be much lower in the first situation than in the |
| Tversky) shows that there are common methods | | | | second. Although proving a causal connection may be |
| people use to "make judgments under uncertainty" | | | | more difficult for the plaintiff in the second situation, |
| (Tversky, Amos and Daniel Kahneman (1974) | | | | jurors will be much more bothered by it, and |
| "Judgment Under Uncertainty: Heuristics and Biases, | | | | therefore, motivated to find a connection. |
| Science, 185, 1124-1131). They call these heuristics, or | | | | Jurors who reject the defense's general causation |
| rules of thumb. Again, while they are not necessarily | | | | argument are not necessarily ignorant or stupid. They |
| rational in the economic sense, they make sense to | | | | may simply be employing forms of reasoning that we |
| the decision-maker. | | | | all use to negotiate everyday life. But among the |
| In a famous example, they point out how many | | | | results of these forms of reasoning are: |
| people are willing to drive across town to save $5 on | | | | 1. A tendency to see patterns and clusters where |
| a $15 calculator, but would not be willing to drive | | | | there is actual randomness (a disease cluster, for |
| across town to save $5 on a $125 coat. Rationally, if | | | | example). |
| the first decision-makes sense then the second | | | | 2. A tendency to believe that any chemical is toxic |
| makes equal sense. We find examples of this same | | | | and that exposure to any amount of that chemical |
| kind of reasoning in the courtroom. Jurors will see a | | | | has the ability to cause any disease. |
| chemical that causes the death in ten people in a | | | | 3. A tendency to trust studies based on small sample |
| million as more dangerous than one that cause one | | | | sizes as well as anecdotal evidence. |
| death in a hundred thousand. | | | | 4. A tendency to ignore the prevalence of a disease |
| Two forms of heuristics stand out in their work in | | | | in the general population. |
| terms of their applicability to science in the | | | | 5. A tendency to confuse correlations between |
| courtroom. The first is the availability heuristic. If it is | | | | exposure to a substance and the presence of a |
| easier for a person to imagine or recall an event then | | | | disease with a causal relationship. |
| the person is more prone to judge the event as | | | | Conclusion |
| more likely to occur. People overestimate the | | | | In everyday life, scientists and lawyers do not |
| frequency of low probability but dramatic hazards. | | | | behave like scientists and lawyers. For jurors a trial is |
| Our research has shown that people overestimate | | | | everyday life. They do not and will not reason like |
| the frequency of deaths from lung cancer in this | | | | experts. To the lawyer and scientist, jurors may be |
| country. The mortality rate from lung cancer for | | | | making mistakes in their reasoning, but they are not. |
| women in 1999 was 40 out of 100,000 (American | | | | They are doing the reasoning of everyday life. How |
| Cancer Society (2003), Cancer Facts and Figures | | | | this is done with scientific evidence can be |
| 2003, p.4). | | | | understood and consequently the evidence can be |
| Our research shows that most people believe the | | | | presented to them in a way that makes sense to |
| mortality rate to be between one and five percent. | | | | everyone, lawyers, scientists, and jurors alike. |
| Other research has shown that people overestimate | | | | |