CORRESPONDENCE Comment on “A systematic

review of the association between pleural plaques and changes in lung function” by Kopylev et al (2014) Kopylev et al1 conducted a meta-analysis of lung function decrements associated with pleural plaques. Several factors indi-cate that this analysis was inappropriate. Although Kopylev et al1 considered study quality, they did not conduct a formal risk-of-bias analysis. Also, several studies did not provide data needed to cal-culate mean differences and SEs of lung function parameters. For these missing data, Kopylev et al1 made assumptions and inputted values that may have biased results. Further, they excluded null studies that did not provide measurements without discussing how this likely impacted the interpretation of results. Most data in the meta-analysis were unadjusted for potential confounding by past asbestos exposure, smoking and body mass index. Kopylev et al1 assumed that confounding factors were similar between comparison groups in each study, but several studies reported substantial differences between exposures and/or smoking (eg, Clin et al2). Kopylev et al1 cited a longitudinal study3 showing lung function decrements over time in a population with pleural plaques. As this study had no comparison population, it is impossible to determine the cause of lung function loss. No othe