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RESEARCH WEEKLY: Lack of consensus on definition of “SMI” within research
By Hope Parker
(April 19, 2023) There is no consistent definition of “SMI,” despite being widely used in scientific, clinical, and policy settings. As “SMI” is not an official diagnostic term, its meaning and characteristics are left to individual researchers and organizations to define. “SMI” can be used to refer to both serious and severe mental illness with no clear differentiation, and, subsequently, the term can easily become convoluted. This lack of consistent definition can lead to variable research about “SMI,” because there is no clear guidance on which individuals are considered to have a serious or severe mental illness.
Treatment Advocacy Center defines severe mental illness as an umbrella term including the severe psychiatric conditions of schizophrenia and associated psychotic disorders, severe bipolar disorder, and major depression with psychotic features. Serious mental illness, on the other hand, is usually defined by impairment. For example, the National Institutes of Mental Health’s definition of serious mental illness is “a mental, behavioral, or emotional disorder resulting in serious functional impairment, which substantially interferes with or limits one or more major life activities.“
In a new study from “Psychiatric Services,” researchers analyzed the definition of “SMI” in 788 scientific papers published from January 2015 to December 2019 that used “SMI” to describe the population being studied. Both the characteristics of “SMI,” such as functional impairment and duration of symptoms, and diagnoses included under the umbrella of “SMI” lacked uniformity, according to their findings, with many of the reviewed studies failing to define “SMI” at all.
Two researchers read each paper, and each recorded the study’s country, type, age group, definition of terminology, and diagnoses included under the “SMI” definition. At a weekly meeting with a third researcher, discrepancies between readers were discussed to ensure accuracy and reliability.
Key Findings
Definitions of “SMI”
Definitions of “SMI” varied substantially across scientific literature, according to the results. Below is a list of how frequently aspects of “SMI” were utilized:
- 41% of studies used “SMI” to reference “severe mental illness,” while 37 % of studies referenced “serious mental illness.”
- 85% of studies failed to fully define “SMI,” meaning there was not specific criteria listed as to what qualifies as “SMI” and examples of which diagnoses are included under the term.
- 37% of studies mentioned specific mental health diagnoses that fall under the term “SMI.”
- 9% of studies included functional impairment in the definition of “SMI.”
- 5% of studies mentioned a duration of time symptoms must have been present (e.g., longer than a year).
Diagnostic characteristics
Studies utilizing the term “SMI” had participants with varying mental illnesses. Below is a list of how frequently each mental health disorder appeared in “SMI” research:
- 62% included participants with schizophrenia or schizoaffective disorder.
- 52% included participants with bipolar disorder.
- 34% included participants with major depressive disorder.
- 33% included participants with other psychotic disorders.
- 14% included participants with other mood disorders.
- 14% included participants with anxiety disorders.
- 14 % included participants with personality disorders.
- 11% included participants with substance use disorders.
Implications
Due to the lack of a widely-used definition, the authors consider the term “SMI” to be unreliable. Within research, this means that it is difficult to determine to whom a study examining “SMI” may apply. This can lead to inconsistencies within research on this term, which can have real-world implications when it comes to policymaking and the distribution of funds.
To solve this problem, the researchers suggest the creation of professional working groups to clearly define and operationalize the term “SMI,” so that its usage is consistent across research, clinical practice, and policy.
Treatment Advocacy Center generally uses the term "SMI" to refer to severe mental illness. However, in research writing, we may use serious mental illness if referring to or summarizing research in which serious mental illness was utilized and most accurately presents the information.
As director of research Elizabeth Sinclair Hancq wrote in a letter to the editor in “Health Affairs” last year, despite the lack of consensus, “SMI” is still an important policy construct. “Appropriate policies for people with mental illness are different than those for people with serious mental illness,” Hancq writes. “Someone living with schizophrenia has unique experiences, treatment needs, and barriers to access compared with someone with a form of mental illness that does not include psychosis.”
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