Citation bias in reported smoking prevalence in people with schizophrenia

Objective: A meta-analysis of 42 studies on tobacco smoking among schizophrenia subjects found an average smoking prevalence of 62% (range=14-88%). Statements are common, however, in the research literature and the media that between 80% and 90% of people with schizophrenia smoke. The purpose of the present paper was therefore to determine if citation bias exists in the over-citation and reportage of studies finding high rates of smoking prevalence in schizophrenia subjects. Methods: Two hypotheses were tested: (i) that studies on the prevalence of smoking in people with schizophrenia reporting high smoking rates would be cited more often than studies reporting lower rates; and (ii) that statements about smoking rates among schizophrenic people on the Internet would report very high rates more often than more realistic, less dramatic rates. Results: A 10% increase in reported prevalence of smoking was associated with a 61% (95% confidence interval (CI)=30-98%) increase in citation rate. Journal impact factor (IF) was significantly associated with citation rate (p=0.001) but the country in which a study was carried out did not have an effect (p=0.90). After adjusting for IF, a 10% increase in prevalence of smoking was associated with a 28% increase (95%CI=1-62%) in citation rate. This bias is mirrored on the Internet, where statements abound about uncommonly highly rates of smoking by people with schizophrenia. Conclusions: Studies reporting very high prevalence of smoking among people with schizophrenia are cited more often than those studies reporting a low prevalence, a result consistent with citation bias. This citation bias probably contributes to the misinformation available on the Internet, and may have adverse policy and clinical implications.