Risk homeostasis theory

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

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. 

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... 

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

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. 

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. 

Changes in the traffic accident record in Japan have been proclaimed by one commentator as totally at variance with the presumed prediction of the risk homeostasis theory (Evans, 1986). Consider, however, the following. 

To an external observer, these measures would seem draconian enough to reduce some people s appetite for driving at all, and for those who still drive to do this in a risky manner. Koshi s observations indicate that the accident toll can be drastically reduced by severely punitive administrative and enforcement measures, provided that such measures are sustained over time, and are further helped along by a weakening economy. To interpret these findings as totally at variance with the presumed prediction of the risk homeostasis theory , would seem totally at variance with the actual course of events. 

Evans, L. 1986. Comments on Wilde s notes on risk homeostasis theory and traffic accident data. Risk Analysis, 6, 103-107. 

McKenna, F.P. 1985. Do safety measures really work An examination of risk homeostasis theory. Ergonomics, 28,489-498. 

Wilde, G.J.S. 1989. Accident countermeasures and behavioural compensation The position of risk homeostasis theory. Journal of Occupational Accidents, 10, 267-292. 

The first scientific attempt to deal with the issue of compensation was the classic field-theoretical study of Gibson and Crooks (1938). One theoretical concept was the field of safe travel and a key observation was the impact of brakes on driver behaviour better brakes could make the field of safe travel—that is, the distance to the car in front—shorter. Nearly 50 years later, the launch of risk homeostasis theory (RHT) gave rise to a profound debate about risk, risk homeostasis and risk compensation (Wilde 1988, 1982 see also Chapter 5). The core issue in the debate was Wilde s determined assertion that all individuals, not only car drivers, carry an inherent target level of risk that they are seeking to maintain or restore. 

Wilde (1982, 1988) Risk homeostasis theory and target level of risk... 

Wilde, G. J, S. (2002). Does risk homeostasis theory have implications for road safety for. Br. 324,1149-1151. 

The best-known motivational model - and the one that has been most frequently challenged — is the risk homeostasis theory of driving behavior. The first formulation of this model was probably Taylor s (1964) risk-speed compensation model, which postulated that drivers adjust their speeds in accordance with the perceived risk. More recently the model has been expanded by Wilde (1998,2002) to include and account for a host of driver behaviors. Because of the controversy it has generated and the research that it has spurred, it will be described here in some detail. According to Wilde, we strive not to minimize risk (or maximize safety), but to reduce (or increase) it to a non-zero level with wdiich we feel comfortable. Because different driving situations have different levels of inherent dangers, we constantly strive to adjust our behavior to maintain a relatively constant risk level. The continuous adjustment process, similar to diat of a room thermostat, is displayed in Figure 3-12. 

Figure 3-12. A schematic representation of Wilde s risk homeostasis theory relating driver behavior to the gap between the driver target risk level and the perceived risk based on actual crash history at the site (Wilde, 1998 2002 with permission from BMJ Publishing Group, Ltd.).

Despite its intuitive appeal, the theory has been challenged by many researchers in the field (Evans, 2004 Fuller, 2005 Haight, 1986 Oneill and Williams, 1998 Robertson, 2002), to the extent of being ludicrous (Robertson, 2002). In brief, the main criticisms of the risk homeostasis theory, summarized by Robertson (2002) are that ... 

Most of the research that supports the risk homeostasis theory is flawed in its design or analysis, and overwhelming contrary findings negate its results. 

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. 

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. 

This theory is based on the assumption that the operator is able to perceive a risk level in the environment that is related to the actual risk level through a delayed feedback. The operator adapts his or her behaviour in such a way that there is a balance between the hazards that the operator is exposed to and what he or she can accept (target level of risk). It follows from this theory that measures to reduce hazards at the workplace will be followed by changed behaviour on the part of the operators such that their perceived level of risk remains the same. The only way to improve safety is to change the operators target risk level. The risk-homeostasis theory was primarily developed for situations where people voluntarily expose themselves to accident risks such as in traffic. We must expect, however, that employees at a workplace also to some extent control the risk that they are exposed to based on their own experiences and preferences. 

---