Schizophrenia cannot be precisely defined because of the diversity of manifestations, courses and outcomes of this mental illness. It has been described as a slowly progressive deterioration of the entire personality, which involves mainly the affective life, and expresses itself in disorders of feeling, thought and conduct, and a tendency to withdraw from reality. In general it constitutes a gross failure to achieve or maintain functioning of an integrated personality. The person becomes unable to cope with problems of living and human relationships; he or she withdraws from reality, becoming refractory to influence and suggestion, with shallow and inappropriate emotional responses, foolish or bizarre behaviour, false beliefs (delusions), false perceptions (hallucinations), and disordered thinking. The condition, previously called Dementia praecox, creates many difficulties for the family of the individual, although the human relationships in that setting may be an important factor in the emergence of it.
An estimated 45 million people are affected by schizophrenia with 4.5 million new cases of schizophrenia and other delusional disorders identified each year. It is estimated that in the USA at any one time there are approximately 1.4 million patients in hospital because of schizophrenia, namely 25% of the hospital population. The average length of stay is 13 years (although the majority leave within one year, large numbers remain until death). In the UK, 60,000 hospital beds are occupied by schizophrenics, and it is estimated that 600,000 others suffer from the disease; approximately 1 person in 100.
Schizophrenia is expected to rise in poor countries to 24.4 million in year 2000. By 2025, 75% of the world's cases are expected to be in these poor countries.