“…Firstly, the Salford study is unique because the numbers of patients is such that the eect on mortality risk of particular variables can be determined while simultaneously controlling for the eects of age, gender and calendar year of follow-up. And secondly, because the cohort was observed between 1968 and 1985 it can help clarify whether mortality risk in OBD has declined throughout the 1970s and 1980s as claimed by some workers (Christie, 1982;Christie and Train, 1984;Wood et al, 1991;Blessed and Wilson, 1982;Oce of Health Economics, 1979).…”