Validation of the smoking habits of a sample of the patient population seen in a pulmonary function laboratory.

From a structured history of 32 current smokers seen in the pulmonary function laboratory of a community hospital, we determined the number of cigarettes they smoked in 24 h. We also asked them to estimate their cigarette butt lengths from a visual model and to collect all cigarette butts over the next 24 h and mail them to us. We counted the butts, individually measured their lengths, and compared these with their previous estimates in order to validate their claims. While in the laboratory, we determined the level of carboxyhemoglobin in the peripheral blood of each patient. Patients tended to estimate the numbers of cigarettes that they smoked in units of five. Light smokers returned more butts and heavy smokers returned fewer butts than the numbers they reported as usually smoking. All patients were able to precisely estimate the average length of their cigarette butts, and they left butts of consistent lengths. There was no association between the numbers of cigarettes smoked and the butt lengths. Carboxyhemoglobin levels were positively associated with the numbers of cigarettes smoked in 24 h and negatively associated with the butt length and the time elapsed since the last cigarette was smoked, but these were not associated with the amount of tar in the cigarettes or with the number of years the person had smoked.