• epidemiology;
  • schizophrenia;
  • self-report;
  • smoking;
  • validity

Aims:  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.

Methods:  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.

Results:  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 (Ptrend < 0.01). In contrast, the stratified data on education level did not indicate any such significant modifying effect.

Conclusions:  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.