Epilepsy is a group of long-term neurological disorders characterized by epileptic seizures. These seizures are episodes that can vary from brief and nearly undetectable to long periods of vigorous shaking. In epilepsy, seizures tend to recur, and have no immediate underlying cause while seizures that occur due to a specific cause are not deemed to represent epilepsy. In most cases the cause is unknown, although some people develop epilepsy as the result of brain injury, stroke, brain cancer, and drug and alcohol misuse, among others. Epileptic seizures are the result of excessive and abnormal cortical nerve cell activity in the brain. The diagnosis typically involves ruling out other conditions that might cause similar symptoms (such as syncope) as well as figuring out whether any immediate causes are present. Epilepsy can often be confirmed with an electroencephalogram (EEG). Epilepsy cannot be cured, but seizures are controllable with medication in about 70% of cases. In those whose seizures do not respond to medication, surgery, neurostimulation or dietary changes may be considered. Not all cases of epilepsy are lifelong, and a substantial number of people improve to the point that medication is no longer needed. About 1% of people worldwide (65 million) have epilepsy, and nearly 80% of cases occur in developing countries. Epilepsy becomes more common as people age. In the developed world, onset of new cases occurs most frequently in infants and the elderly; in the developing world this is in older children and young adults, due to differences in the frequency of the underlying causes. About 5–10% of all people will have an unprovoked seizure by the age of 80, and the chance of experiencing a second seizure is between 40 and 50%. In many areas of the world those with epilepsy either have their ability to drive restricted or disallowed, but most are able to return to driving after a period of time without seizures.