A case-control study was conducted to determine whether passive smoke exposure (environmental tobacco smoke) was associated with development of asthma. Newly diagnosed asthma cases were compared with a random sample of non-asthma controls drawn from the same population that produced the cases. Cases and controls were asked to complete questionnaire with a series of questions assessing their past exposure to passive (environmental) tobacco smoke either at home or in other settings.If people with asthma are more aware of their exposure to passive smoke than those without asthma, what type of bias would this produce?