Optimistic Bias
William M. P. Klein

Most research has investigated optimistic biases at the group level, which has been sufficient given the predominant focus on which types of events, comparative targets, and other factors elicit the most bias. However, in order to establish the utility of this construct in the domain of health, it is necessary to measure optimistic bias at the level of the individual. Given the difficulties of doing so, research taking this approach is in its infancy. For the most part, the evidence so far suggests that optimistic biases may be harmful.

Several studies show that optimistically biased individuals know less about health threats (Radcliffe & Klein, 2002 xClose
Radcliffe, N. M., & Klein, W. M. P. (2002). Dispositional, unrealistic, and comparative optimism: Differential relations with knowledge and processing of risk information and beliefs about personal risk. Personality and Social Psychology Bulletin, 28, 836-846. ), are less attentive and more defensive in response to new health information (Avis, Smith, & McKinlay, 1989 xClose
Avis, N. E., Smith, K. W., & McKinlay, J. B. (1989). Accuracy of risk perceptions of heart attack risk: What influences perceptions and can they be changed? American Journal of Public Health, 79, 1608-1612. ; Radcliffe & Klein, 2002 xClose
Radcliffe, N. M., & Klein, W. M. P. (2002). Dispositional, unrealistic, and comparative optimism: Differential relations with knowledge and processing of risk information and beliefs about personal risk. Personality and Social Psychology Bulletin, 28, 836-846. ; Wiebe & Black, 1997 xClose
Wiebe, D. J., & Black, D. (1997). Illusional beliefs in the context of risky sexual behaviors. Journal of Applied Social Psychology, 27, 1727-1749. ), and endorse myths such as the notion that lung cancer risk is influenced substantially more by genetics than by smoking (Dillard, McCaul, & Klein, 2005 xClose
Dillard, A. J., McCaul, K. D., & Klein, W. M. P. (2005). Some consequences of unrealistic optimism about smoking. Manuscript under review. ). These studies typically control for obvious confounds such as educational level. Other studies have shown that optimistically biased individuals may have higher risk factors for disease such as smoking (Strecher, Kreuter, & Kobrin, 1995 xClose
Strecher, V. J., Kreuter, M. W., & Kobrin, S. C. (1995). Do cigarette smokers have unrealistic perceptions of their heart attack, cancer, and stroke risks? Journal of Behavioral Medicine, 18, 45-54. ) and high cholesterol (Radcliffe & Klein, 2002 xClose
Radcliffe, N. M., & Klein, W. M. P. (2002). Dispositional, unrealistic, and comparative optimism: Differential relations with knowledge and processing of risk information and beliefs about personal risk. Personality and Social Psychology Bulletin, 28, 836-846. ).

Perhaps most importantly, many studies show that optimistically biased individuals engage in more risk-increasing behaviors such as unprotected sexual intercourse (Burger & Burns, 1988 xClose
Burger, J. M., & Burns, L. (1988). The illusion of unique invulnerability and the use of effective contraception. Personality and Social Psychology Bulletin, 14, 264-270. ) and alcohol abuse (Klein et al., 2005 xClose
Klein, W. M. P., Geaghan, T. R., & MacDonald, T. K. (2005). Unplanned sexual activity as a consequence of alcohol use: A prospective study of risk perceptions and alcohol use among college freshmen. Unpublished manuscript. ); one study using a national sample found that optimistically biased smokers were less likely to intend to quit (Dillard et al., 2005 xClose
Dillard, A. J., McCaul, K. D., & Klein, W. M. P. (2005). Some consequences of unrealistic optimism about smoking. Manuscript under review. ). Importantly, one study showed that HIV seropositive individuals who were optimistically biased about their AIDS risk engaged in more health-protective behaviors (Taylor et al., 1992 xClose
Taylor, S. E., Kemeny, M. E., Aspinwall, L. G., Schneider, S. G., Rodriguez, R., & Herbert, M. (1992). Optimism, coping, psychological distress, and high-risk sexual behavior among men at risk for acquired immunodeficiency syndrome (AIDS). Journal of Personality and Social Psychology, 63, 460-473. ), suggesting again that there may be several other factors that determine whether optimistic biases lead to risk-increasing or risk-decreasing behavior. For example, optimistic biases may be more adaptive when health outcomes are reversible, and when the individuals are already coping with a medical problem (Klein & Steers-Wentzell, in press xClose
Klein, W. M. P., & Steers-Wentzell, K. L. (in press). On the physical health costs of self-enhancement. To appear in E. Chang (Ed.), Self-criticism and self-enhancement: Theory, research, and clinical implications. Washington, DC: American Psychological Association. ). Importantly, most of these studies are correlational, making it difficult to pinpoint optimistically biased risk perceptions as a direct cause of behavior.