RESEARCH WEEKLY: What is the True Prevalence of Schizophrenia in the United States?
By Elizabeth Sinclair Hancq
Last week, the United States Census Bureau released its official U.S. population estimate after undertaking a count of every single person living in the United States, a procedure that is conducted once every 10 years. The results indicate that as of April 1, 2020, there were 331,449,281 individuals living in the United States, a 7.4% increase since 2010.
In order to determine how many Americans are living with severe mental illness, one needs to apply a prevalence estimate of the percentage of people living with these psychiatric disorders to the U.S. adult population. However, there currently is no recent prevalence estimate of severe mental illness in the United States.
The Treatment Advocacy Center uses the prevalence rate of 1.1% of adult individuals with schizophrenia and 2.2% with severe bipolar disorder to come up with our estimate of 8.3 million individuals living with severe mental illness in 2019 (2.8 million with schizophrenia and 5.5 million with severe bipolar disorder). These prevalence estimates were published by the National Institute of Mental Health (NIMH) based on data from a study completed in 1985.
However, in early 2018, the NIMH changed the prevalence estimates on their website despite no new research published on the topic. The new published prevalence estimate suggested there were only 750,000 individuals living with schizophrenia in the United States, effectively eliminating two million individuals with this illness with the stroke of a pen. In an article Treatment Advocacy Center founder Dr. E. Fuller Torrey and I published in Psychiatric Times, we called attention to the NIMH change and questioned the justification for significantly reducing the prevalence estimate of schizophrenia without any new data or research.
New proposed methodology for estimating the schizophrenia prevalence rate
An article published in Schizophrenia Research in April 2021 proposes a new method for calculating the prevalence rate of schizophrenia in the United States. In his article, author Dr. Ramin Mojtabai of the Johns Hopkins Bloomberg School of Public Health in Baltimore suggests that because national population surveys miss individuals with schizophrenia who are homeless, in long-term hospitals or jails and prisons, relying on a statistical method applied to administrative data such as Medicaid and Medicare data is a more reliable way to determine the prevalence rate of schizophrenia. In fact, this statistical method, referred to as the multiplier method, is often utilized in epidemiological research for hard-to-reach populations, according to Dr. Mojtabai.
The multiplier method to determine the prevalence rate of schizophrenia proposed by Dr. Mojtabai is as follows:
Proportion of people with a schizophrenia diagnosis among Medicaid-Medicare enrollees divided by the proportion of people with schizophrenia who have Medicaid-Medicare coverage multiplied by the total population of enrolled Medicaid-Medicare individuals.
Dr. Mojtabai applies this method to the dually eligible Medicaid-Medicare population because of the relatively higher prevalence of schizophrenia in this population compared to the general population.
Using this method, the prevalence estimate of schizophrenia is 1.624%, or 3.8 million adults based on data from the 2010 census. This rate is significantly higher than other schizophrenia prevalence estimates from previous studies, including being more than 2.5 times what is published on the NIMH website. The age breakdown of the 2020 census to determine the adult population has not yet been released but undoubtedly will result in an even higher estimate for today’s population.
Dr. Mojtabai notes that this schizophrenia estimate is still likely an underestimate because it misses incarcerated adults who lose Medicaid coverage and those who have never had a treatment contact that would be captured in Medicaid records. However, “the findings suggest a much higher annual prevalence of treated schizophrenia in the US than that suggested by the previous general population surveys and analyses based on different insurance databases,” Dr. Mojtabai concludes.
No Mental Health Awareness without data
As we enter Mental Health Awareness Month, it is important to consider all that we still need to know about the most severe psychiatric disorders. The total number of people who live with a condition is one of the most basic epidemiological statistics, but this data remains elusive for severe mental illness. Beyond personal experiences, mental health awareness is only as good as the information on which it is based.
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