Prevalence quantifies the proportion of individuals in a population who have a disease during a specific time-period while incidence refers to the number of new cases of disease that develop in a population during a specific time-period while. In disorders of short duration incidence and prevalence rates may be similar, however with disorders of long duration such as with schizophrenia there can be variation between the two.

What is the evidence regarding prevalence of schizophrenia in refugees?

High quality evidence finds the overall prevalence of psychotic disorders, mostly schizophrenia spectrum, is 1.5% in refugees and asylum seekers. Studies were undertaken in Australia, Germany, Italy, Lebanon, Norway, United Kingdom, and the United States of America. Refugees were from Azerbaijan, former Yugoslavia, Middle East, Africa, Palestine, and Russia.

April 2022

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Prevalence represents the overall proportion of individuals in a population who have the disorder of interest. It is different from incidence, which represents only the new cases that have developed over a particular time period. Point prevalence is the proportion of individuals who have the disorder at a given point in time. Period prevalence is the proportion of individuals who have the disorder over specific time periods. Lifetime prevalence is the proportion of individuals who have ever had the disorder. Lifetime morbid risk also includes those who had the disorder but were deceased at the time of the survey.

What is the evidence for the prevalence of PTSD in refugees?

High quality evidence finds the overall prevalence of PTSD is around 31% in refugees and asylum seekers. Rates were highest in women, in refugees from Africa, and in smaller studies. Rates varied according to diagnostic scale, with the Clinician Administered PTSD Scale showing highest rates (40%), and the Mini-International Neuropsychiatric Interview showing lowest rates (26%).

Moderate to high quality evidence finds the prevalence of PTSD in war-affected refugees and citizens is also around 31%. Rates were highest in those exposed to recent conflict. They were also highest in those exposed to torture, to more traumatic events, and to political terrorism. They were highest in people from Cambodia, Bosnia, Kosovo, and Africa.

Moderate quality evidence finds the prevalence of PTSD in adult Syrian refugees living in Western or Middle Eastern countries is 43%. The prevalence of PTSD in Iraqi refugees living in Western countries is up to 37%.

Moderate quality evidence finds the prevalence of PTSD in child and adolescent refugees is around 23%. Rates were highest in those displaced for less than two years and in those with an insecure visa status.

April 2022

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The incidence of bipolar disorder refers to how many new cases 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. Differences in the incidence of a disorder can provide clues to its possible causes. 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.

What is the evidence for incidence of bipolar disorder in migrant populations?

Moderate quality evidence suggests no increases in the incidence of bipolar disorder in migrant populations compared to non-migrant populations.

October 2021

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The term “migrant” usually refers to first generation migrants – people with a foreign birth place, and studies have assessed whether migration is related to risk of bipolar disorder.

Any association observed between migrant status and increased risk of mental disorders has stimulated a great deal of 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 for migrant status as a risk factor for bipolar disorder?

Moderate quality evidence finds a small increase in the risk of bipolar disorder or affective psychosis after migration.

October 2021

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Incidence refers to how many new cases 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. Incidence is usually reported as the number of new cases per 100,000 people per year. Alternatively some studies present the number of new cases that have accumulated over several years against a person-years denominator. This denominator is the sum of individual units of time that the persons in the population are at risk of developing schizophrenia. It takes into account the size of the underlying population sample and its age structure over the duration of observation. 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 who were born within a certain time period (an age cohort) and where they were born. Cross linking this information with a mental health register can be used to identify those who received treatment for schizophrenia over particular times. This can provide information regarding the incidence of schizophrenia within different groups.

What is the evidence for incidence of schizophrenia in refugees?

Moderate quality evidence finds small to medium-sized effects of increased incidence of schizophrenia and other psychotic disorders in refugee groups after migration (up to 10 years) compared to native-born populations and non-refugee immigrants. The incidence was highest in refugee men and in refugees from the Middle East.

April 2022

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Prevalence measures the proportion of individuals who have a disorder at a particular point in time (point prevalence) or during a specified period (annual prevalence, lifetime prevalence) and this may vary across regions. It is distinct from incidence, which refers to how many new cases there are per population in a specified time period. Lifetime prevalence is the number of individuals in a population that at some point in their life have experienced schizophrenia compared to the total number of individuals.

What is the evidence for prevalence rates in migrant populations?

Moderate quality evidence found increased prevalence of schizophrenia in migrant populations compared to native-born populations.

April 2022

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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 finds the incidence rate of schizophrenia is higher in migrants than in native-born populations. This is found in both first and second generation migrants, and particularly in migrants with black skin and in those living in the UK, The Netherlands, and Scandinavian countries.

Please also see the topic on incidence of schizophrenia in refugees.

April 2022

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The term “migrant” usually refers to first generation migrants; people with a foreign birth place, however some studies also include their locally-born offspring, or second generation migrants. Any association found between migrant status and increased risk of schizophrenia has stimulated a great deal of research and explanatory hypotheses, including the 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 differences in underlying genetic vulnerability across cultures.

What is the evidence regarding migration as a risk factor for schizophrenia?

Moderate quality evidence finds increased incidence and prevalence of schizophrenia in migrants compared to native-born individuals. The risk remains after adjusting for age, sex, and socio-economic status. The increased incidence was found in people who migrated between infancy and adolescence, but not during early adulthood (19-29 years).

There was a medium-sized, increased risk of non-affective psychosis (including schizophrenia) in refugees compared to native-born people, a small to medium-sized increased risk of non-affective psychosis in non-refugee migrants compared to native-born people, and small increased risk of non-affective psychosis in refugees than in non-refugee migrants.

There was increased incidence of schizophrenia in both first and second generation migrants, particularly in migrants from developing countries and in migrants with black skin. There was a large increased risk of schizophrenia in black Caribbean and black African migrants and their descendants in the UK compared to the white British population. Asian migrants in the UK show a medium-sized increased risk of schizophrenia compared to the white British-born population.

April 2022

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