Risk homeostasis

The risk-homeostasis theory focuses on the degree of caution exercised by individuals in the handling of accident risks. Accident rates are, according to the risk homeostasis theory, determined mainly by the accident risks that people on average are willing to take (Wilde, 1982). It is a rather pessimistic perspective as to the effects of non-motivational accident counter-measures. Elimination or reduction of hazards in the workplace will result in decreased caution on the part of the individual. This behavioural change will by and large offset the effects of the measures. 

This theory has primarily been developed to explain traffic-safety data. In the traffic arena, risk-taking is to a large extent voluntary. In industry, on the other hand, behaviour including risk-taking is subject to management supervision and control. We must, however, expect that the same processes are present in industry but to a lower degree, since they represent basic human traits. 

The immediate impression is that the risk-homeostasis theory may be in conflict with the basic theories and principles of SHE information systems. We tend to evaluate SHE information systems by looking into the safety measures that have been implemented as a result. They are often of the non-motivational type that according to the risk-homeostasis theory will have marginal effect. In general, the SHE-information-system approach does not involve any particular preferences as to the selection of remedial actions. They may be motivationally oriented as well as non-motivational. 

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The following section will address six personality traits that may affect human reliability, namely, motivation, risk taking, risk homeostasis, locus of control, emotional control, and type "A" versus type "B" personality. 

The somewhat controversial theory of risk homeostasis is relevant to a discussion of risk taking. RHT was developed initially in the area of driving behavior (Wilde, 1984). The theory states that accident rates are not determined by actual levels of intrinsic risk but by the levels of risk acceptable to individuals in the situation. The theory implies that people adjust their risk-taking behavior to maintain a constant level of perceived risk. Thus, if improved safety measures are introduced (e.g., better guarding, improved protection systems then individuals will behave in a more risky fashion in order to maintain their accustomed levels of risk. 

McKenna, F. P. (1985). Do Safety Measures Really Work An Examination of Risk Homeostasis Theory. Ergonomics 28,489-498. 

Wilde, G. J. S. (1984). Evidence Refuting the Theory of Risk Homeostasis A Rejoinder to Frank P. McKenna. Ergonomics 25, 879-890. 

Risk Homeostasis The theory that an operator will attempt to maintain a stable perception of risk following the implementation of new technology that increases the safety of a human-machine system. The theory predicts that operators will take greater risks where more safety devices are incorporated into the system. 

Wilde G.J.S., 1982. The theory of risk homeostasis implications for safety and health, Risk Analysis 2, pp. 209-225. 

The importance of understanding new employee safety expectations is further reinforced if expectations are considered within the framework of risk homeostasis theory. Wilde and colleagues developed risk homeostasis theory (see Wilde et al. 2002 Simonet and Wilde 1997) which proposes that as safety feamres (expected or real) are added to a system, users tend to increase their exposure to risk because they feel better protected. For example, if a new employee expects that equipment is well maintained, they may use equipment without checking its functionality. Similarly, if a new employee expects that co-workers will remove hazards from the workplace, or not create hazards, they may not actively engage in as much monitoring for hazards. Put it another way, incorrect safety expectations can lead a new employee to take unexpected risks. 

Table 3.2 is an attempt to show the general nature of safety expectations across the four categories of new employee and also shows the associated level of safety expectation-driven risk exposure. The expectation-driven risk exposure level is based on the predictions of risk homeostasis theory, where less realistic expectations about safety aspects in a workplace may lead an individual to engage in behaviors which turn out to be risky, or not to engage in behaviors, such as monitoring and being careful, which will help ensure safety. 

Wilde, G.J.S., Target Risk. PDE Publications, Toronto (1994). A thorough review of the risk homeostasis literature. A book to make you think about the effectiveness of safety interventions aimed at human behaviour. 

Will the introduction of the system result in a change in behaviour that could result in an increased demand on the system to mitigate risk For example, risk homeostasis theory (Wilde, 2001) suggests that individual has an inbuilt target level... 

Stanton, N.A. and Glendon, A.I. (1996). Risk homeostasis and risk assessment. Safety Science, 22(1-3), 1-13. 

Trimpop, R. M. 1996. Risk homeostasis theory Problems of the past and promises for the future. Safety Science, 22,119-130. 

FIGURE 3,1 Risk homeostasis process. (From Wilde, G.J.S. The theory of risk homeostasis Implications for safety and health. Risk Analysis, 1982, 2(4), 209-225. Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced with permission.)... 

If there is a utility model determining target risk, then it should be feasible to formulate that model in mathematical terms, or alternatively to derive the utilities and trade-offs through the standard game-type approach used in stated preference studies. However, Wilde (1988) denies that it is possible to derive quantitative utilities [T]he target level of risk is thought of as a construct that people arrive at in an intuitive manner, not as the result of explicit calculation of probabilities of particular outcomes and their positive or negative values (p. 443). Thus, we have a model whose main mechanism cannot be verified empirically because it is only an intuitive construct. Therefore, it can be concluded that what we have here is more assertion than model. (For more on risk homeostasis, the reader is directed to Chapter 5.)... 

Wilde, G.J.S. 1988. Risk homeostasis theory and traffic accidents Propositions, deductions and discussion of dissension in recent reactions. Ergonomics, 31(4), 441-468. 

Feelings of risk homeostasis Risk monitor model Multiple comfort zone model DiC model... 

FIGURE 4.4 Feelings of risk homeostasis model. (From Kinnear, N. 2009. Driving as You... 

Accident countermeasures such as mandatory seatbelt wearing, airbags installed in cars, antilock brakes, and so on lead to behavioural adaptation, and this is because they fail to lower the level of risk people are willing to accept. According to risk homeostasis theory (RHT Wilde, 1978, 1982), the added sense of control and of being protected that such measures provide leads drivers to adopt one form or other of behavioural adjustment for the purpose of satisfactions other than safety, and per capita risk essentially remains the same. 

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