Cannabis’s Link to Schizotypy: Phenomenon, Measurement Bias, or Delusion?

Links between cannabis use and psychosis continue to generate research and media attention. Cannabis users have outscored non-users on the Schizotypal Personality Questionnaire-Brief (SPQ-B) by a small amount in multiple studies, but previous work on biased items suggests that the groups do not differ if these items are removed. The present study examined links between schizotypal personality, as measured by the SPQ-B, and cannabis use in a large sample recruited from Amazon’s MTurk platform. Over 500 participants (72.5%) reported lifetime cannabis exposure, 259 participants (36.7%) reported current cannabis use, and on average, used 3.5 days per week. Users and non-users failed to differ significantly on total SPQ-B scores or any of the three established subscales, with effect sizes all lower than d = .20. The null results inspired a re-examination of the SPQ-B’s factor structure, which identified a novel 3-factor solution (difficulty opening up to others, hyperawareness, and odd or unusual behavior). Only the “odd or unusual behavior” factor showed cannabis-related differences (g = .234), but a differential item functioning test revealed that one item on that subscale showed potential bias against users. Removing this item dropped the group differences to a non-significant g = 0.149. These results suggest that links between schizotypy and cannabis require cautious interpretation with careful attention to potential measurement bias. In addition, the Schizotypal Personality Questionnaire-Brief might have an alternative factor structure that could help answer important questions in psychopathology.