The case crossover design was introduced in 1991 by Maclure M (Am J Epidemiol 1991;133:144-53) to study the transient effect of brief exposure on the occurrence of a rare acute-onset disease. The argument is that if there are precipitating events, these events should occur much more frequently during a period immediately prior to the onset of disease than at a similar period which is more distant from the disease onset. For example, it has been reported that physical stress and mental stress may trigger sudden cardiac death. If this is true, one would find that sudden cardiac death occurred more frequently during or shortly after strenuous physical activity, or that there was an increase in informant-reported life stress either acutely before sudden cardiac death or during the weeks before the event. Another example is the alcohol consumption and injury. The effect of alcohol is transient and alcohol use is usually associated with injury. Therefore, one would expect that the alcohol consumption prior to injury increases the risk of injury.

PowerPoint file of this lecture - http://www.pitt.edu/~super7/0011-1001/0821.ppt