缘起
Storytelling在经济学写作中的重要性不言而喻，是每一位经济学研究者的必修课，而引言部分的作用则是将文章的故事脉络呈现给读者。因此，想设置这样一个栏目，和大家一起精读解析论文引言的写作技巧，初衷是慢慢积累也许有朝一日能够把引言写好，如果能给大家带来一点点的外部性，就再好不过了。
今天随机找了一篇文章，Guojun He 2020发表在JDE上的文章：秸秆燃烧，PM2.5以及死亡率。且先拿它试试手。
- He, Guojun, Tong Liu, and Maigeng Zhou. "Straw Burning, PM2.5 and Death: Evidence from China," Journal of Development Economics, 2020, 145: 102468.
摘要：本文利用卫星数据研究农业秸秆燃烧并估算其对中国空气污染和健康的影响。研究发现，秸秆燃烧增加了颗粒物污染，导致人们死于心肺疾病。PM2.5每增加10μg/m^3，死亡率增加3.25%。农村地区的中老年人对秸秆燃烧污染尤为敏感。对中国秸秆回收项目的进一步分析表明，将这些项目推广到所有秸秆燃烧地区所带来的健康效益大于成本。
第一段
首先介绍背景，第一句Farmers often burn agricultural straw residues from crops such as wheat, rice, maize, and cotton in situ after harvest. 向不熟悉背景的读者介绍 秸秆燃烧到底是什么：“农民经常在收获后就地焚烧小麦、水稻、玉米和棉花等农作物的秸秆残留物。” （插一句：实际上，燃烧秸秆的处理方式在中国更为普遍，但并不科学，极大加剧空气污染，雾霾严重程度，虽然已有许多更优的处理秸秆的方式，但新技术难以在农村普及，观念的转变困难，亟需设立新的激励机制。
Farmers often burn agricultural straw residues from crops such as
wheat, rice, maize, and cotton in situ after harvest. Straw burning is
particularly prevalent in developing countries that rely heavily on agricultural production and is a major cause of seasonal air pollution
(Andreae and Merlet, 2001; Gadde et al., 2009; Rangel and Vogl, 2019).
秸秆焚烧在严重依赖农业生产的发展中国家特别普遍，是造成季节性空气污染的主要原因(Andreae and Merlet, 2001; Gadde et al., 2009; Rangel and Vogl, 2019)。这句话开始将秸秆燃烧和空气污染联系起来，开门见山，不绕弯子。如果是中文期刊，开头还要用一大段介绍政策背景，实际上这些背景放在Section 2详细介绍更好一些，我们需要时时提醒自己，引言的每一句话都有一个明确的指向，就是让读者快速明白文章的贡献，动机和意义。告诉别人你的文章为什么好，为什么好到让大家愿意花时间一看。因此，引言的每一句话，都不应该是废话。
However, effective regulations on straw burning are rare and the lack of
scientific evidence on how straw burning affects people’s health can
make the government reluctant to design and enforce strict regulations.
However（However大多数情况下后面跟着的内容就是文章的创作动机或贡献）,作者做这篇文章的Motivation主要有两个：（1）秸秆燃烧是空气污染的主要来源，但现有相关的法律法规很少；（2）目前还没有证据表明秸秆燃烧是否以及如何影响人们健康，这可能使得政府不愿设立并执行相关法律法规。
接着引出本文的贡献：（1）利用中国数据估计秸秆燃烧对空气污染和死亡率的影响，（2）并量化中国在秸秆回收政策的潜在收益。
In this study, we estimate the impacts of straw burning on air pollution
and mortality using data from China and try to quantify the potential
benefits of China’s recent efforts in straw recycling.
第二段
介绍文章使用数据的独特性。包括2013-2015年中国秸秆燃烧卫星数据（秸秆燃烧），1650个地面监测站收集到的当地空气质量数据（空气污染），中国疾病预防控制中心的疾病监测点系统(DSPS)的四分之一中国人口的死亡记录（死亡率）。
Our analysis is based on a novel panel dataset that assembles detailed
information on straw burning, air pollution, and mortality in China. High-resolution satellite image data are used to identify the exact locations of straw burning in China from 2013 to 2015. Straw burning data
are then linked to local air quality data collected from 1650 ground-level
monitors. Death records from a quarter of the Chinese population are
obtained from the Disease Surveillance Point system (DSPS) of China’s
Center for Disease Control and Prevention, which contains information on gender, age group, and cause of death at the county level for the same
period.
第三段
介绍使用这些数据做了什么？发现了什么？（本文的研究问题及发现）
With these data matched at the county level, we then estimate how straw burning affects air pollution and mortality.
本文的研究问题：估计了秸秆燃烧对空气污染和死亡率的影响。
Our baseline results
show that 10 additional straw fires within 50 km of a county center will
lead to a 4.79 μg/m3 (or 7.62%) increase in monthly fine particulate
matter (PM2.5, diameter < 2.5 μm) and a 1.56% increase in all-cause
mortality in Chinese counties. Using straw burning as an instrumental
variable, we further estimate that a 10 μg/m3 increase in monthly PM2.5
can lead to a 3.25% increase in mortality. Heterogeneity analyses reveal
that straw burning pollution primarily increases cardiorespiratory mortality, and has a strong impact on people over 40 in rural and poor areas,
but has no statistically significant impact on younger people.
句式大抵如此：Our baseline results show that、 we further estimate that、Heterogeneity analyses reveal that……
研究发现：（1）在县城中心50公里范围内再发生10起秸秆火灾，将导致PM2.5增加4.79μg/m3(或7.62%)，中国各县的死亡率上升1.56%（2）。以秸秆燃烧为工具变量进一步估计发现，PM2.5月浓度每增加10μg/m3可导致死亡率增加3.25%。（3）异质性分析显示，秸秆燃烧污染主要增加心肺死亡率，对农村和贫困地区40岁以上人群影响较大，但对年轻人影响不显著。
第四段
强调本文在因果识别上存在的担忧以及解决方法：找啊找啊找IV。
JDE对这种微观实证，因果识别清晰的文章比较青睐。
The key concern of our baseline IV estimate is that straw burning may affect human health through channels other than air pollution. For example, local governments may implement straw burning regulations that are endogenous to local population health. It is also possible that straw burning can create temporary income shocks to farmers, as the
activity is associated with harvesting.
本文的IV识别还存在两个问题：（1）桔梗燃烧可能不是通过空气污染而是其他途径影响人类健康，例如，地方政府可以实施与当地人口健康有关的秸秆焚烧条例。（2）另外，秸秆燃烧也可能对农民造成暂时的收入冲击，因为该活动往往在丰收之后。
To address these issues, we adopt
two augmented IV strategies, which together lend additional credibility
to our baseline finding. In our first augmented strategy, we use non-local straw burning to instrument local air pollution (conditional on local
straw burning). Non-local straw burning is an appealing instrument for
air pollution because the burning behaviors of non-local farmers are
typically not subject to the local government’s control. In the second
strategy, we follow Rangel and Vogl (2019) and explore different wind
patterns for identification. We separate straw burning from upwind and
downwind areas and use the difference in the coefficients between upwind and downwind fires to isolate the pollution effect from the potential
income effect. The identification relies on the fact that upwind and
downwind straw fires have asymmetric impacts on air pollution, but have
symmetric impacts on local people’s income. In both exercises, we obtain
estimates that are quantitatively similar IV to the baseline model, suggesting the endogeneity of straw burning is not a big concern in our
research context
为解决这一问题，作者进一步采用两个IV解决内生性。（1）非本地农民焚烧秸秆（non-local straw burning），不受当地政府控制。（2）将秸秆燃烧与上风和下风区域分开，并利用上风和下风火灾系数的差异将污染效应与潜在收益效应隔离开来。
结果与基本回归系数大小相差不大，说明秸秆燃烧的内生性不是一个大问题。
第五段
进一步对2016年出台的秸秆回收政策进行评估，说明政策的有效性：受补贴省份的相对于非补贴省份，PM2.5年均浓度下降了4.33 μg/m3，避免每年1.89万人过早死亡。
Based on our findings, we then evaluate China’s recent straw recycling policy, launched in 2016. We find that subsidizing straw recycling
effectively improved air quality and the estimated health benefits could
outweigh the costs by an order of magnitude. Specifically, using a
Difference-in-Differences (DiD) approach, we show that the number of
straw fires in subsidized provinces dramatically declined after the policy
(by 153 a year), relative to the non-subsidized provinces, and this change
brought down the annual average PM2.5 concentration by 4.33 μg/m3.
These estimates imply that the straw recycling policy could have averted
18,900 pre-mature deaths annually in China
第六、七、八段
总结对现有文献的三个贡献，英文期刊常用三大段讲文章的主要贡献，而中文往往在一段中写完，每一个贡献用一句话来写，实际上还是远远没有得到足够的重视。我们在写引言时，如果能在初稿形成时用三大段写明文章的贡献，会更加清楚文章在现有文献中的位置和贡献，这非常有利于深刻理解自己的文章。甚至解决大部分时候自己的内耗问题，觉得自己的文章没有意义，实则是因为我们做得还远远不够。
首先，本文补充了关于秸秆燃烧影响的文献。这是一支比较小众的文献脉络， Rangel and Vogl (2019)； Graff
Zivin et al. (2019)； Lai et al. (2018)做了相关的工作。但这篇文章区别于Rangel and Vogl (2019)之处在于（1）……。（2）……。这里的逻辑在于，写该领域的重要文献做了什么，尽管有做得非常相似的文章也无所谓，写出来，然后说清楚，你区别于他的贡献在哪里。
We contribute to the literature in three ways. First, this paper adds to
the emerging literature on the impacts of straw burning (e.g. Graff Zivin
et al., 2019; Lai et al., 2018; Rangel and Vogl, 2019). In this thin line of
literature, Rangel and Vogl (2019) are the first to link agricultural
burning to health outcomes. Exploiting the interactions between wind
patterns and sugarcane harvest fires in Brazil, they show that
late-pregnancy exposure to upwind fires decreases birth weight, gestational length, and in-utero survival, but not early neonatal survival. Graff
Zivin et al. (2019) adopt a similar approach and find that air pollution
from agricultural fires lowers the cognitive performance of students in a
high-stakes test in China. Lai et al. (2018) investigate how agricultural
fire affects cognitive function among the Chinese people and show that
more straw burning reduces old people’s cognition and memory. Our
main contributions beyond Rangel and Vogl (2019) are that (1) we are
able to investigate the impacts of straw burning on mortality for different
age groups, which helps highlight the most vulnerable people to straw
burning pollution, and (2) we apply our estimates to assess a recent straw
recycling policy implemented by the Chinese government.
其次，本文发现空气污染效应存在显著的城乡异质性。由于数据限制，农村人口数据缺失，现有文献估计不准确，如Zhou et al. (2015) and Fan et al. (2020)。
Second, we find significant rural-urban heterogeneity in the air
pollution effect. Due to data limitations, rural residents have largely been
ignored in existing air pollution studies. Notable exceptions include Zhou
et al. (2015) and Fan et al. (2020). In both studies, the authors find that
air pollution effects are larger and statistically significant in rural areas,
but small and statistically insignificant in urban areas. While our research
context is different from the previous studies, we also find that straw
burning and air pollution significantly increase the mortality of rural
residents and poor residents, but not that of urban or rich residents. These
results together suggest that better socio-economic conditions can mitigate the health damage of air pollution.
最后，本文发现近期出台的秸秆回收补贴政策显著减少了秸秆焚烧活动，为制定有效的秸秆焚烧法规提供了重要启示，为其他存在类似农业焚烧问题的农业经济体提供参考。这是本文的impliaction。
Finally, we show that China’s recent straw-recycling subsidy significantly reduced straw burning activities, which provides important insights into designing effective straw burning regulations. Historically, the
Chinese government relied on command-and-control regulations to reduce straw burning. Due to the high enforcement costs, however, these policies were not very successful. In contrast, providing subsidies to farmers and recycling companies immediately led to less burning and improvement in air quality. The incentive-based approach seems to outperform the command-and-control approaches in our research context. These findings can be referenced by other agrarian economies with similar agricultural burning issues.
第九段
最后一段介绍各个章节的内容安排,The rest of this paper is structured as follows. Section 2……，Section 3……，Section 4…… 都是形式化的内容，大同小异。
The rest of this paper is structured as follows. Section 2 introduces the practice of straw burning in China and reviews the current literature. Section 3 describes the data on straw burning, deaths, pollution and weather, followed by an introduction on data compilation, a summary of key variables, and descriptive analyses. Section 4 discusses our empirical strategy. Section 5 reports the main findings. Discussions of caveats and robustness checks follow in Section 6. Section 7 explores a variety of heterogeneities in the health effects of straw burning pollution. Section 8 estimates the impact of the straw recycling policy and conducts an exploratory benefit-cost analysis. Section 9 concludes.
引言就这么结束了，希望以后还有时间细细精读文献，每个阶段看文献的目的大不相同，做实证的时候可以速读，只看实证怎么做，写的时候又不一样，引言摘要等，都有值得细细斟酌之处，无奈我的水平只能到此为止