Validity of self-reported smoking in schizophrenia patients

It is important to evaluate smoking status among schizophrenia patients because such patients are highly inclined to take up smoking, but only a few studies have focused on the validity of self-reported smoking in relation to schizophrenia. The aim of the present study was therefore to determine the validity of self-reported smoking and to investigate whether self-reported smoking is biased in schizophrenia patients.

A total of 158 schizophrenia patients answered self-rated questions of smoking status, and the level of carbon monoxide (CO) in expired air was measured. The relationship of the self-reported smoking to the CO levels was determined, and interaction of the disease duration and education level on this relationship was evaluated using correlation and receiver operating characteristic analyses.

The CO levels in the expired air were found to be positively related to the self-reported data (P < 0.01). The stratified data on the duration of schizophrenia indicated that the positive relationship between self-reported smoking and the CO concentration became less obvious with the increase in duration of schizophrenia (P(trend) < 0.01). In contrast, the stratified data on education level did not indicate any such significant modifying effect.

Although self-reporting is useful for evaluating smoking status, psychiatrists should use objective methods of measurement to assess the smoking status of chronic schizophrenia patients.