Discussion 是一篇 SCI 論文中最難寫的部分，該部分需要作者對比領域前人所做的研究，結合本研究，並對未來方向進行科學展望 ，Discussion 是作者科研水平的直觀體現。
Discussion 的好壞很大程度上決定 SCI 能否被接收。
本文以 2019 年 8 月 13 日發表在 JAMA 上的一篇文章為例，和大家分享下 SCI 論文中 Discussion 的寫作套路。
Discussion 原文
Higher residential concentrations of O3, PM2.5, 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.
闡述研究的主要發現，Discussion 寫作固定套路，首段一般描述研究的主要發現，特別注意：不要重述結果，該段不要有任何解釋性的話語。
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 PM2.5 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，對本研究結果進行描述和評價。
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, PM2.5 exposure leads to neutrophili pulmonary inflammation and oxidative stress,28 and in healthy adults, controlled exposure to PM2.5 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
對研究的結果進行合理的解釋，通過引證流行病學，毒理學研究，動物模型等對結果可能的機制進行評價，增加結果的科學性。
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
與前人所做的研究做對比，增加本研究結果的可靠性，相同點或不同點，同意之前的結果還是有所進步。
常用語有：
- 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
結合文獻對研究結果進行解釋，讓研究結果可以作為論據支持論文的論點。
Higher exposures to PM2.5 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
作者對論文結果進行評價分析，並與以前出版的文獻結果進行比較，是否一致。
Unlike O3 and NOx, PM2.5 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 PM2.5 at baseline but not during follow-up. Baseline measures likely reflect exposure at and prior to baseline, particularly for PM2.5 concentrations, which declined substantially over the 10 years of follow-up. In addition, the changes in scanner technology over follow-up as PM2.5 concentrations decreased may have made the follow-up analyses less sensitive for emphysema progression than the baseline analyses。
通過引證文獻，對論文結果進行解釋說明。
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, PM2.5, NOx, and black carbon, have been associated consistently with respiratory events,10,12 relatively few studies have reported a longitudinal association between O3, PM2.5, 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 PM2.513 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.
闡述研究的主要優勢，對於首例研究的表達需謹慎，只要在查詢大量文獻後，確保事實如此，才用 first XX study to assess/investigate.... 表達。
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.
其他研究優勢的說明，討論部分中闡述優缺點時，可以採用 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.
闡明研究尚存的一些不足或侷限性，條理清晰。並對存在的不足進行一定合理的解釋，而不是一味羅列研究的不足點。
接下來，和大家分享下 Discussion 的幾點注意事項：
1. Discussion 部分寫作，所有數據都要源於論文的 Results，不能引入新的數據。當然，引用他人的文獻除外，但不要過於重複 Results 內容。
2. Discussion 要特別注意邏輯性，很多作者寫經常跑偏了。應按照結果的主次進行分段討論，講述每個結果表示什麼，與前人發表的數據對比，引證文獻加以說明。
3. Discussion 中應正視研究的不足。像 LANCET，NEJM，JAMA 這些頂刊作者也會在論文中相當謙虛的說明研究的侷限，對未來可以改進的地方進行討論和展望，化被動為主動，建議大家學習。
4. 寫 Discussion 語法上儘量使用主動句，語句要簡練。
總結一下，本文以 JAMA 發表的文章為例，向大家分享了 SCI 論文 Discussion 的寫作，建議作者在平時
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關鍵字: Discussion study percent
