Good governance at the World Bank.

202 www.thelancet.com Vol 371 January 19, 2008 Chen refers to several potential confounding factors. We believe that, in this population, educational level is a better measure of socioeconomic status than annual income, and is what we adjusted for. The relation between abdominal obesity and COPD is not consistent, and many studies suggest that it is related to a restrictive rather than obstructive pattern of lung disease. Furthermore, one of the studies quoted by Chen suggests that abdominal obesity is related to reduced lung function in men, but not women. The high proportion of women in our population suggests this is unlikely to be a problem in our study. Similarly, although there is some evidence that dietary intake is important, it is not conclusively shown to be a risk factor for COPD, and diff erent dietary factors are implicated in diff erent studies. However, as indicated in our discussion, although our study supports that passive smoking exposure does contribute to COPD, we believe that other factors must also play a part among never smokers. We therefore do intend to examine the role of dietary factors in future analyses. Urinary cotinine refl ects recent exposure to tobacco smoke (typically over the past 2–3 days), and does not take account of longer term exposure. COPD is a chronic disease that develops over many years and it would be inappropriate to link current cotinine levels with disease. We used urinary cotinine data only to validate smoking status. Chen correctly points out that our sample is not necessarily representative of the population of Guangzhou or China, as discussed in our paper. However we believe that our estimation of 1·9 million deaths is, if anything, conservative, being based on risk estimates derived from a relatively healthy population older than 50 years (whereas COPD aff ects many under 50 as well), and on a likely underestimate of the true population of China. We concur with Chen’s comments on the need for campaigns to reduce smoking in China, and indeed our team is actively supporting such initiatives.