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July 21, 2021

Changes in Attributable Fractions and Causal Inference for Schizophrenia and Other Psychiatric Outcomes

Author Affiliations
  • 1Harvard T. H. Chan School of Public Health, Boston, Massachusetts
JAMA Psychiatry. Published online July 21, 2021. doi:10.1001/jamapsychiatry.2021.1256

In this issue of JAMA Psychiatry, Hjorthøj et al1 use Danish national registry data from 1972 through 2016 to examine longitudinal associations between cannabis use disorder and schizophrenia after controlling for potential confounders. They carried out numerous sensitivity analyses2 and further report attributable fractions for schizophrenia attributable to cannabis use disorder. The article1 makes 2 distinct contributions. First, it adds to the prior evidence base3,4 concerning potential associations of cannabis use with schizophrenia, with analyses indicating a relatively stable 4-fold increase in schizophrenia risk associated with cannabis use disorder. Second, they estimate that the proportion of schizophrenia cases attributable to cannabis use disorder increased from approximately 2% in 1972 through 1995 to 8% by 2010. In this Editorial, I will discuss the various sources of evidence for potential causal associations of cannabis use with schizophrenia, comment on different types of attributable fractions over time, and discuss the interpretation and potential implications of the results from Hjorthøj et al.1

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