so的疑问？

Tobacco smoking (Chapter 20) is responsible for threequarters of lung cancers worldwide and 90% of lung cancers in countries where smoking is common, and, on a population scale, lung cancer rates mirror smoking rates with an approximate lag time of 20 years. Both the number of cigarettes smoked per day and the duration of being a smoker are positively correlated with the risk of developing lung cancer, although the latter is the stronger association.Quitting smoking has the predictable opposite effect, with the risk of developing lung cancer decreasing with every year of continued abstinence, although the risk never falls as low as that for a lifetime nonsmoker.

Smoking prevalence amongst men was at a peak approximately 20 years before the peak for women, so at present the lung cancer incidence in men is declining, whereas in women the incidence continues to increase. The greater incidence of lung cancer in women is not caused solely by differences in smoking prevalence, but on a dose-for-dose basis women also seem to be more susceptible to the carcinogens found in cigarette smoke, with an odds ratio of between 1.2 and 1.7 compared with men for developing lung cancer with equivalent smoking habits.

全球75%的肺癌及吸烟常见国家90%的肺癌中，吸烟是罪魁祸首（见第二十章），通过对整个人口的分析，肺癌发病率大致等于吸烟率，肺癌发病大约滞后吸烟20年。每天吸烟的数量及烟龄都与患肺癌的风险呈正相关，但烟龄与患肺癌风险的相关性更强。戒烟具有可预见的降低罹患肺癌风险的效果，这种风险会随着戒烟的持续而逐年降低，但不会完全达到与终身非吸烟者完全相同的低风险水平。

相比女性，男性的吸烟率达峰时间约早20年，因此目前男性的肺癌发病率正在下降，而女性的发病率继续上升。女性肺癌发病率增加并不完全是由于吸烟情况的差异，从剂量角度来看，与等效吸烟的男性相比，女性似乎也更易受到香烟烟雾中致癌物质的影响，女性患肺癌的优势比是男性的1.2～1.7（译者注：优势比是病例组中暴露人数与非暴露人数的比值除以对照组中暴露人数与非暴露人数的比值，是反映疾病与暴露之间关联强度的指标）。

Smoking prevalence amongst men was at a peak approximately 20 years before the peak for women, so at present the lung cancer incidence in men is declining, whereas in women the incidence continues to increase？so 是表示因果关系吗？怎么理解这个因果关系？哪来的因果关系？