Reliability of data on smoking habit and coffee drinking collected by personal interview in a hospital-based case-control study

A study on the reliability of information on smoking habits and coffee drinking collected via interview was conducted among 500 subjects enrolled in a case-control study on bladder cancer in Brescia, North Italy. A total of 215 cases (incident and prevalent) and 285 controls were interviewed personally in the hospital setting by a first interviewer, and then reinterviewed by telephone by either the same interviewer or another one. Agreement between the first and second interview was evaluated using the kappa statistic and the intra-class correlation coefficient and via multiple logistic regression modelling. No important differences in reliability were found according to sex, education or case/control status, while agreement was better among subjects below 65 than among older ones, and among incident than prevalent cases. A slightly better agreement was found among subjects interviewed twice by the same interviewer than those interviewed by two different individuals, which may reflect the presence of inter-observer reliability for the latter. Overall, these results show a very high reliability of data on smoking and a fairly high reliability regarding coffee drinking as collected through face-to-face interviews.