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What is incidence and how is it relevant to schizophrenia?

Incidence refers to how many new cases of schizophrenia there are per population in a specified time period. It is different from prevalence, which refers to how many existing cases there are at a particular point in time, or over a lifetime. Incidence is usually reported as the number of new cases per 100,000 people per year, but this can vary. Differences in the incidence of a disorder can provide clues to its possible causes. For example, a population register with information gained from consensus data helps to identify all adults in a defined area who were born within a certain time period (a cohort). Cross linking this information with a mental health register for the cohort can be used to identify people who received treatment for schizophrenia over particular times. This information provides the incidence of schizophrenia for various age groups within that cohort.

The term “migrant” usually refers to first generation migrants – people with a foreign birth place, however some studies also include locally born offspring, or second generation migrants in their analyses. Any association observed between migrant status and increased incidence of schizophrenia has stimulated a great deal of research and explanatory hypotheses, including additional stress relating to migration and settling into a new country, and possible issues with discrimination. Other explanations include a tendency for at-risk individuals to migrate, and underlying genetic variances across cultures.

What is the evidence on incidence of schizophrenia in migrant populations?

Moderate to high quality evidence indicates increased incidence of schizophrenia in both first and second generation migrant populations, particularly for migrants from developing countries with high or medium income and for migrants with black skin.

Moderate quality evidence finds a large increased incidence of schizophrenia in black Caribbean and black African migrants in the UK, and in their descendants, compared to the white British population, while Asian migrants showed a medium-sized increased risk of schizophrenia compared to the white British population.

Moderate quality evidence finds small to medium-sized effects of increased incidence of schizophrenia and other psychotic disorders in refugee groups after migration, compared to native-born populations and non-refugee migrants. This risk was highest in refugee men and in refugees from the Middle East.

January 2019

Last updated at: 12:31 am, 29th March 2019
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