An investigation of late-onset schizophrenia found that 28% of patients had the onset of illness after age 44 years and 12% after age 63 years, based on 470 chart reviews of patients who had sought psychiatric help during a period of 20 years (Castle and Murray, 1993). Although the majority of patients have an early age at onset, a certain subgroup of patients may have a distur-bance that meets all the criteria of schizophrenia with onset in their forties or later.
The phenomenology of late-onset compared with early-onset schizophrenia may be distinct, with later-onset cases hav-ing a higher level of premorbid social functioning and exhibiting paranoid delusions and hallucinations more often than formal thought disorder, disorganization and negative symptoms. Stud-ies have also shown a high comorbid risk of sensory deficits, such as loss of hearing or vision, in patients with late-onset schizo-phrenia. Specifically, late-onset patients are more likely to report visual, tactile and olfactory hallucinations and are less likely to display affective flattening or blunting. One of the most robust finding among the late-onset cases is the higher prevalence seen in women. This does not appear to be due to sex differences in seeking care, societal role expectations or delay between emer-gence of symptoms and service contact.
A large body of data suggests that although men and women have an equivalent lifetime risk; the age at onset varies with sex. Strong evidence that onset of schizophrenia is on average 3.5 to 6 years earlier in men than in women.
There is undoubtedly a subgroup of patients who have a later onset of illness (after age 45 years), and this subgroup is made up predominantly of women Among these female schizo-phrenia patients, there is a higher incidence of comorbid affective symptoms. When the effects of gender, premorbid personality, marital status and family history of psychosis on the age at on-set were removed in a reanalysis of the WHO 10-country study data, there was a significant attenuation of the gender differences (Jablensky and Cole, 1997).
The ECA data have shown that there is no significant difference in the prevalence of schizophrenia between black and white per-sons when corrected for age, sex, socioeconomic status and mari-tal status (Robins and Regier, 1991). This finding is significant because it refutes prior studies that have shown the prevalence of schizophrenia to be much greater in the black population than in the white population.
A study of marriage and fertility rates of individuals with schizo-phrenia compared with the general population showed that, on average, by the age of 45 years, three times as many of those with schizophrenia as of the general population are still unmar-ried (40% of men and 30% of women with schizophrenia are still single by age 45). Studies have also shown that fertility rates are lower in patients with schizophrenia compared with the general population. These observations may be related, and further in-vestigation of the role of premorbid function, negative symptoms and fertility rates, including rates among unmarried patients, is warranted. With the advent of the newer and more effective an-tipsychotic medications, and their increased use in first episode patients, it is possible that we may witness improved fertility and marriage rates in patients with schizophrenia.
For many years, epidemiological studies revealed a higher inci-dence and prevalence of schizophrenia in groups with lower so-cioeconomic status. In the past half century, studies have found that the actual incidence of schizophrenia does not vary with so-cial class, based on first admission rates, adoption studies and a series of studies examining the social class of the fathers of peo-ple with schizophrenia. When these findings did not validate the original theory, it became clear that lower socioeconomic status was more a result than a cause of schizophrenia. This led to the acceptance of the downward drift hypothesis, which stated that because of the nature of schizophrenic symptoms, people who develop schizophrenia are unable to attain employment and posi-tions in society that would allow them to achieve a higher social status. Thus, these patients drift down the socioeconomic ladder, and because of the illness itself they may become dependent on society for their well-being.
That season of birth differs between individuals with schizophre-nia and the general population has by now gained wide accept-ance. This factor has been studied in the 20th century, with the predominant view that the birth rate of people with schizophrenia is highest in late winter. Torrey and colleagues (1997) confirmed this, reviewing approximately 250 studies and concluding that there is an excess of schizophrenia births during winter. In fact, there is approximately a 5 to 8% greater likelihood for individu-als with schizophrenia to be born during winter months com-pared with the general population. This higher incidence of win-ter births has been found in both hemispheres, offering further evidence that this phenomenon is related to the colder months rather than specific calendar months.