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##### Risk, Probability and Judgment

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**Today’s Topics**• What is risk? • How do we perceive risk? • How do we measure risk? • What is risk assessment? • How does risk affect our decision making? Risk, Probability, and Judgment**Making Informed Decisions**• Define the problem or choice • Gather information • Evaluate the information • Make a decision Risk, Probability, and Judgment**Energy Decision-making**• Each source of energy has trade-offs • Some good things, some bad things associated with each • Most people feel that having abundant energy is worth some risks Risk, Probability, and Judgment**What is Risk?**• Risk is essentially the chance that something bad could occur • Everything we do exposes us to some risk • Walking across the street • Going down a flight of stairs • Driving around the block • Playing sports • Generating electricity Risk, Probability, and Judgment**Risks of Nuclear Energy**• All energy sources have related risks • Questions to be answered about nuclear energy: • Do the benefits outweigh the risks? • How do the risks of nuclear energy compare to risks related to using other sources to generate electricity? • What are the risks of not using/having electricity? Risk, Probability, and Judgment**Judging Risk**• Today, we know a lot about many kinds of risks • Advances in science • Availability of information through mass media • As individuals and groups we make decisions based on how risky we think certain things are • Different people see different things as dangerous or acceptable Risk, Probability, and Judgment**How We Perceive Risk**• A variety of factors influence how risky we believe certain activities to be • Control • Dread • Natural vs. man made • Familiar vs. new • Choice • Awareness • Sudden vs. gradual Risk, Probability, and Judgment**Risk Assessment**• A branch of science that determines actual risks involved in various technologies and activities • Aimed at protecting public health and improving public safety • Scientists and decision-makers compare risks by looking at their relative probabilities. Risk, Probability, and Judgment**Probability**• Probability is a number that quantifies how likely something is to occur • Percentages and probabilities are related but not the same. • Percentages are a mathematical statement of how many times out of 100 something happens. • Probabilities refer to just one occurrence. Risk, Probability, and Judgment**Probability**• Scientists determine probabilities through repeated observations or controlled experiments • The number of times that a specific outcome occurs, divided by the total number of times the experiment is repeated, is the probability that the specific outcome will occur. Risk, Probability, and Judgment**Probability**• Random events like flipping a coin cannot be predicted with certainty. • Every time the coin is flipped, there is a 0.50 probability of heads and a 0.50 probability of tails. • If a lot of flips in a row land heads up, the probability that the next flip will be tails is still 0.50. Risk, Probability, and Judgment**Calculating Probability**• Then the probability of each outcome is 1 divided by the number of possible outcomes. • For example: the probability of drawing the ace of spades from an ordinary deck of cards is 1/52. Risk, Probability, and Judgment**Think about it…**• What is the probability of drawing any ace on any one draw? • What is the probability of drawing 5 cards of the same suit? Risk, Probability, and Judgment**Health and Safety Risks**• It is often harder to determine probability of health and safety risks for people • May not be enough information • May not be possible to test all aspects of the system • Certain are rules used to make reasonable predictions Risk, Probability, and Judgment**Health and Safety Risks**• Rules used by decision makers for determining what is “safe” • One in a million • Does not increase the health risk of the population by more than one chance in a million • ALARA • As low as reasonably achievable Risk, Probability, and Judgment**Health and Safety Risks**• Limitations to knowing risk: • To know risk of “new” technology, we need to know what risk was before • Risk studies are often based on studies of large numbers of animals • Biological differences between rats and mice and humans • Not socially acceptable to test things on large numbers of humans Risk, Probability, and Judgment**Accepting Risk**• Deciding on whether a risk is acceptable involves weighing consequences and values • Sometimes it is very expensive to reduce the risk even a small amount Risk, Probability, and Judgment**Making Societal Decisions**• Many questions—none of them simple • What is the consequence of the risk—loss of money, illness, or death? • How large are the consequences? (costs, number of people affects, size of environment effected) • Do the risks and benefits fall on different people? • Do the risks fall on the decision-makers or on others? • How are decisions made? • What are the alternatives? Risk, Probability, and Judgment**Words to know**• Benefits • Biased information • Consequences • Human-made risk • Natural risk • Probability • Percentage • Risk assessment • Risks • Societal decisions • Values Risk, Probability, and Judgment