顶刊里 Discussion 的写作套路，好像也没那么难…

Discussion 是一篇 SCI 论文中最难写的部分，该部分需要作者对比领域前人所做的研究，结合本研究，并对未来方向进行科学展望，Discussion 是作者科研水平的直观体现。

Discussion 的好坏很大程度上决定 SCI 能否被接收。

本文以 2019 年 8 月 13 日发表在 JAMA 上的一篇文章为例，和大家分享下 SCI 论文中 Discussion 的写作套路。

图片来源：JAMA

Discussion 原文

Higher residential concentrations of O₃, PM_2.5, and NOx at study baseline, of black carbon averaged from 2006 to 2008, and of O₃ and NOx assessed over study follow-up were significantly associated with greater increases in percent emphysema, assessed via CT imaging, over a median of 10 years. Findings were most robust and of greatest magnitude for O₃. Because percent emphysema is related to respiratory symptoms, hospitalizations,⁷ and mortality even among individuals without airflow obstruction,^4,6 these associations in a community-based population demonstrate novel evidence that air pollution contributes to worsening lung health.

阐述研究的主要发现，Discussion 写作固定套路，首段一般描述研究的主要发现，特别注意：不要重述结果，该段不要有任何解释性的话语。

Despite existing regulations to prevent short-term excursions of O₃ levels, long-term average concentrations of O₃, which were associated with changes in lung structure and function, did not decline during the years of observation. Absent new control strategies, these levels are not expected to decline as climate change advances. ²⁵ This contrasts with the observed trends in PM_2.5 and NOx that highlight the success of past regulatory initiatives to control these 2 pollutants. Because long-term concentrations of O₃ at current levels were strongly and consistently associated with both progression of emphysema and decline in lung function in this study, more effective control strategies to reduce O₃ concentrations may be needed to protect lung health.

承接第一段，对本研究结果进行描述和评价。

Ground-level O₃ is a powerful oxidizing agent and common air pollutant worldwide. Toxicologic studies have shown that O₃ causes persistent pulmonary inflammation and structural alterations throughout the lung that may play a role in chronic lower respiratory disease, including emphysema.²⁶ In a mouse model, exposure to O₃ for 6 weeks induced a chronic inflammatory process, with increased protease expression, epithelial apoptosis and alveolar enlargement, and destruction, mimicking emphysema.²⁷ In animals, PM_2.5 exposure leads to neutrophili pulmonary inflammation and oxidative stress,²⁸ and in healthy adults, controlled exposure to PM_2.5 leads to increased systemic inflammation and endothelial microparticles, including those of lung origin.²⁹ This may be relevant because endothelial apoptosis causes emphysema in animals and endothelial microparticles have been linked to lower lung function and, specifically, percent emphysema in individuals with mild COPD and smokers without COPD.³⁰

对研究的结果进行合理的解释，通过引证流行病学，毒理学研究，动物模型等对结果可能的机制进行评价，增加结果的科学性。

The current study found that faster progression of percent emphysema and decline in FEV1 were significantly associated with long-term O₃ concentrations among the subset of participants with airflow limitation at baseline. This finding is consistent with prior studies demonstrating worse outcomes related to air pollution in patients with lung disease31 and supports the conclusion in the 2013 EPA Integrated Science Assessment that individuals with lung disease are a high risk group for O₃-related health effects.³²

与前人所做的研究做对比，增加本研究结果的可靠性，相同点或不同点，同意之前的结果还是有所进步。

常用语有：

• This finding was consistent with prior studies...；

• Consistent with the prior studies , our study indicated/showed that...；

• Our findings were in line with the prior studies...

Findings for O₃ and loss of lung function were greater among current smokers, perhaps because of additive effects of airway inflammation and oxidative stress.³³

结合文献对研究结果进行解释，让研究结果可以作为论据支持论文的论点。

Higher exposures to PM_2.5 and NOx at baseline and NOx (and no other pollutants) over follow-up were also significantly associated with faster emphysema progression. When all pollutants were considered together, there was evidence that the association for O₃ was of the greatest magnitude, which is consistent with other literature,¹² and for an additive effect of copollutants, which is consistent with animal studies.³³

作者对论文结果进行评价分析，并与以前出版的文献结果进行比较，是否一致。

Unlike O₃ and NOx, PM_2.5 exposure over follow-up was not significantly associated with emphysema progression. Development of emphysema can be a slow, lifelong process and, once initiated, additional areas of emphysema in the adjacent lung can be produced from biomechanical forces, even in the absence of further exposures, such as cigarette smoke.³⁴ These findings might explain the increased rate of emphysema progression significantly associated with PM_2.5 at baseline but not during follow-up. Baseline measures likely reflect exposure at and prior to baseline, particularly for PM_2.5 concentrations, which declined substantially over the 10 years of follow-up. In addition, the changes in scanner technology over follow-up as PM_2.5 concentrations decreased may have made the follow-up analyses less sensitive for emphysema progression than the baseline analyses。

通过引证文献，对论文结果进行解释说明。

While O₃ exposure was significantly associated with decline in lung function, the other pollutants were not; statistical power for spirometry was smaller than for percent emphysema on CT because the number of observations for spirometry were less than half those for percent emphysema and occurred during the latter period of follow-up when nonozone pollutant concentrations had declined. While air pollutants, including O₃, PM_2.5, NOx, and black carbon, have been associated consistently with respiratory events,^10,12 relatively few studies have reported a longitudinal association between O₃, PM_2.5, and NOx and decline in lung function in older adults, and findings have not been completely consistent. Single site studies have reported longitudinal associations between PM_2.5¹³ and black carbon³⁵ and a faster decline in lung function, and a larger multi-center study in Europe found PM₁₀ to be associated with a faster lung function decline.³⁶ However, another large European study did not find any longitudinal associations between air pollutants and lung function decline.³⁷

To our knowledge, this is the first longitudinal study to assess the association between long-term exposure to air pollutants and progression of percent emphysema on CT in a large, community-based multiethnic cohort.

阐述研究的主要优势，对于首例研究的表达需谨慎，只要在查询大量文献后，确保事实如此，才用 first XX study to assess/investigate.... 表达。

Other strengths of this study include the large sample size, the long period of follow-up, and the fine-scale assessment of residential level outdoor air pollution concentrations from cohortspecific monitoring and advanced statistical modeling.

其他研究优势的说明，讨论部分中阐述优缺点时，可以采用 there are several strengths in our study, Firstly... Secondly, Another strength... Lastly... 等固定套路。

Limitations

This study has several limitations. First, outdoor air pollution concentrations, especially in the case of O₃, may not fully reflect individual air pollution exposures and dose in all microenvironments³⁸; outdoor concentrations do not explain all variation in indoor concentrations, and most individuals spend the majority of their time indoors.³⁹ Second, percent emphysema was measured only in the lower two-thirds of the lung. However, percent emphysema measured in the lower two-thirds of the lung correlates well with full-lung percent emphysema (ICC, 0.93) in this cohort and a cohort of smokers,¹⁸ and percent emphysema measured on cardiac scans was associated with dyspnea, spirometric obstruction, and mortality in this cohort.^4,8 Third, CT scanners changed over the 18 years of data collection; however, analyses using an advanced image processing approach designed to account for scanner variation yielded similar results, as did sensitivity analyses using various approaches to adjust for stratification by scanner type (eTables 4 and 5 in the Supplement). There is debate about the optimal parameterization of the histogram of the lung attenuation; however, sensitivity analyses using PD15 yielded consistent results. Fourth, no volume correction of CT data was performed,⁴⁰ given the debate over its utility and the partial lung imaging; however, results were consistent when participants with a difference greater than 20% in lung volume on CT scans were excluded.

阐明研究尚存的一些不足或局限性，条理清晰。并对存在的不足进行一定合理的解释，而不是一味罗列研究的不足点。

接下来，和大家分享下 Discussion 的几点注意事项：

1. Discussion 部分写作，所有数据都要源于论文的 Results，不能引入新的数据。当然，引用他人的文献除外，但不要过于重复 Results 内容。

2. Discussion 要特别注意逻辑性，很多作者写经常跑偏了。应按照结果的主次进行分段讨论，讲述每个结果表示什么，与前人发表的数据对比，引证文献加以说明。

3. Discussion 中应正视研究的不足。像 LANCET，NEJM，JAMA 这些顶刊作者也会在论文中相当谦虚的说明研究的局限，对未来可以改进的地方进行讨论和展望，化被动为主动，建议大家学习。

4. 写 Discussion 语法上尽量使用主动句，语句要简练。

总结一下，本文以 JAMA 发表的文章为例，向大家分享了 SCI 论文 Discussion 的写作，建议作者在平时多写多练，不断提升科研写作能力！

图片来源：作者提供