The psychological approach began with research in trying to understand how people process information. These early works maintained that people use cognitive heuristics in sorting and simplifying information, leading to biases in comprehension. Later work built on this foundation and became the psychometric paradigm. This approach identifies numerous factors responsible for influencing individual perceptions of risk, including dread, novelty, stigma, and other factors. Research also shows that risk perceptions are influenced by the emotional state of the perceiver. The valence theory of risk perception only differentiates between positive emotions, such as happiness and optimism, and negative ones, such as fear and anger. According to valence theory, positive emotions lead to optimistic risk perceptions whereas negative emotions influence a more pessimistic view of risk. Research also has found that, whereas risk and benefit tend to be positively correlated across hazardous activities in the world, they are negatively correlated in people's minds and judgements. Heuristics and biases The earliest psychometric research was done by psychologists Daniel Kahneman and Amos Tversky, who performed a series of gambling experiments to see how people evaluated probabilities. Their major finding was that people use a number of heuristics to evaluate information. These heuristics are usually useful shortcuts for thinking, but they may lead to inaccurate judgments in some situations – in which case they become cognitive biases. Representativeness: is usually employed when people are asked to judge the probability that an object or event belongs to a class / processes by its similarity: insensitivity to prior probability insensitivity to sample size misconception of chance insensitivity to predictability illusion of validity misconception of regression Availability heuristic: events that can be more easily brought to mind or imagined are judged to be more likely than events that could not easily be imagined: biases due to retrievability of instances biases due to the effectiveness of research set biases of imaginability illusory correlation Anchoring and Adjustment heuristic: people will often start with one piece of known information and then adjust it to create an estimate of an unknown risk – but the adjustment will usually not be big enough: insufficient adjustment biases in the evaluation of conjunctive and disjunctive event (conjunction fallacy) anchoring in the assessment of subjective probability distributions Asymmetry between gains and losses: People are risk averse with respect to gains, preferring a sure thing over a gamble with a higher expected utility but which presents the possibility