Smoking and inequalities

Abstract

Prabhat Jha and colleagues1Jha P Peto R Zatonski W Boreham J Jarvis MJ Lopez AD Social inequalities in male mortality, and in male mortality from smoking: indirect estimation from national death rates in England and Wales, Poland, and North America.Lancet. 2006; 368: 367-370Summary Full Text Full Text PDF PubMed Scopus (319) Google Scholar report in a four-country study that most social inequalities in adult male mortality during the 1990s were due to smoking.1Jha P Peto R Zatonski W Boreham J Jarvis MJ Lopez AD Social inequalities in male mortality, and in male mortality from smoking: indirect estimation from national death rates in England and Wales, Poland, and North America.Lancet. 2006; 368: 367-370Summary Full Text Full Text PDF PubMed Scopus (319) Google Scholar They, and commentator Michael Marmot,2Marmot M Smoking and inequalities.Lancet. 2006; 368: 341Summary Full Text Full Text PDF PubMed Scopus (49) Google Scholar are rightfully cautious about the indirect method used in this analysis. We have used direct methods to estimate the contribution of smoking to socioeconomic and ethnic inequalities in mortality in New Zealand.3Blakely T Wilson N The contribution of smoking to inequalities in mortality by education varies over time and by sex: Two national cohort studies, 1981–84 and 1996–99.Int J Epidemiol. 2005; 34: 1054-1062Crossref PubMed Scopus (34) Google Scholar For the 1996–99 period, smoking contributed 21% to the gap between 45–74-year-old men with post-school qualifications and those with none. The corresponding figure for women was 11%. Our other work suggested that only 5–10% of the larger inequality in mortality between Māori and non-Māori individuals was due to smoking, despite large differences in smoking prevalence.4Blakely T Fawcett J Hunt D Wilson N What is the contribution of smoking and socioeconomic position to ethnic inequalities in mortality in New Zealand?.Lancet. 2006; 368: 44-52Summary Full Text Full Text PDF PubMed Scopus (100) Google Scholar This estimate contrasted with a much greater estimated contribution by the Ministry of Health using Jha and colleagues' indirect method. Why? First, the relative risk from smoking among Māori is lower than among non-Māori,5Hunt D Blakely T Woodward A Wilson N The smoking-mortality association varies over time and by ethnicity in New Zealand.Int J Epidemiol. 2005; 34: 1020-1028Crossref PubMed Scopus (36) Google Scholar highlighting the risk of assuming that relative risks observed in the US Cancer Prevention Study will also apply to populations in other countries. Second, the differences in lung cancer mortality between Māori and non-Māori (threefold to fivefold) are, in all likelihood, greater than can be explained by smoking alone, violating an underlying assumption of the indirect method. Direct methods are preferable where local data permit, and indirect methods must be treated cautiously. Although smoking is an extremely important contributor to health inequalities, we concur with Marmot2Marmot M Smoking and inequalities.Lancet. 2006; 368: 341Summary Full Text Full Text PDF PubMed Scopus (49) Google Scholar that there are also other major determinants of health inequalities. We declare that we have no conflict of interest.