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 re-interviewed 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.