The label “OR (odds ratio)” was erroneously introduced into the headings to tables 3 and 4 in the paper by Aldington et al (Thorax 2007;62:1058–63). In table 3, the numbers in the columns refer to the estimates of the difference of the particular measurement of respiratory function between those who do and those who do not smoke tobacco, and those who do and do not smoke cannabis, respectively. The heading in table 4 refers incorrectly to OR for association between tobacco pack years or cannabis joint years and the measurement of respiratory function. The numbers in the columns refer to the change in the particular measurement of respiratory function per unit change of pack years and joint years respectively. The “OR” label should be omitted from these tables.