Citation bias in reported smoking prevalence in people with schizophrenia

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.

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.

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.

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.