in health-promoting behaviors. Cues to action can be internal or external. Physiological cues (e.g., pain, symptoms) are an example of internal cues to action. External cues include events or information from close others, the media, or health care providers promoting engagement in health-related behaviors. Examples of cues to action include a reminder postcard from a dentist, the illness of a friend or family member, mass media campaigns on health issues, and product health warning labels. The intensity of cues needed to prompt action varies between individuals by perceived susceptibility, seriousness, benefits, and barriers. For example, individuals who believe they are at high risk for a serious illness and who have an established relationship with a primary care doctor may be easily persuaded to get screened for the illness after seeing a public service announcement, whereas individuals who believe they are at low risk for the same illness and also do not have reliable access to health care may require more intense external cues in order to get screened. Self-efficacy Self-efficacy was added to the four components of the HBM (i.e., perceived susceptibility, severity, benefits, and barriers) in 1988. Self-efficacy refers to an individual's perception of his or her competence to successfully perform a behavior. Self-efficacy was added to the HBM in an attempt to better explain individual differences in health behaviors. The model was originally developed in order to explain engagement in one-time health-related behaviors such as being screened for cancer or receiving an immunization. Eventually, the HBM was applied to more substantial, long-term behavior change such as diet modification, exercise, and smoking. Developers of the model recognized that confidence in one's ability to effect change in outcomes (i.e., self-efficacy) was a key component of health behavior change. For example, Schmiege et al. found that when dealing with calcium consumption and weight-bearing exercises, self-efficacy was a more powerful predictors than beliefs about future negative health outcomes. Rosenstock et al. argued that self-efficacy could be added to the other HBM constructs without elaboration of the model's theoretical structure. However, this was considered short-sighted because related studies indicated that key HBM constructs have indirect effects on behavior as a result of their effect on perceived control and intention, which might be regarded as more proximal factors of action. Empirical support The HBM has gained substantial empirical support since its development in the 1950s. It remains one of the most widely used and