Impact when receiving a diagnosis: additive and multiplicative effects between illness severity and perception of control.

Based on Lazarus' transactional model of stress, this study examined how the information provided in a medical diagnosis (the severity of the illness, the effectiveness of the treatment and the self-efficacy to follow this treatment) are combined to generate perception of stress. Twenty-seven scenarios were presented to 152 volunteer students and their level of perceived stress was recorded. Results revealed that the lack of efficacy of the treatment raises the perception of stress proportionally to the different degrees of illness severity, but having a low perceived ability to follow the treatment triggers high levels of stress, particularly when the diagnosis is serious.