Generally, two types of events are encountered in health research: non-reversible events and reversible events. Non-reversible events are those events which are chronic in nature and occur to an individual only once (e.g. hypertension, AIDS, diabetes and cystic fibrosis). While other types of events are reversible event which are acute in nature and can occurs to an individual more than once. Reversible event can further be bifurcated as multiple events and recurrent events. Multiple events are those repeated events that are not of exactly same type but somewhat related, such as repeated hospitalization due to different reasons (hospitalization due to road accident, hospitalization due to fall, hospitalization due to fever, etc.). Unlike multiple events, recurrent events are those repeated event, which are of same type such as acute exacerbations in asthmatic children, seizures in epileptics, low back pain in women, skin cancer, myocardial infarctions, migraine pain, and sports injuries.