第3节 前言
与撰写其他类型的论文类似，这里也许要提供相关信息，使读者了解本综述开展的大背景及原因。前言中，需要对本综述相关的文献进行回顾、分析和总结，进而说明本领域未知或需要进一步探索的地方，最后引出所要开展的综述内容，说明该综述如何填补现阶段知识的未知点。值得一提的是，在撰写综述的前言时，一定要对既往已经存在的类似综述进行回顾和总结，进而说明开展本综述的必要性和重要性。
这里，也会涉及一些常见的术语，例如研究问题（research question），研究目的或研究目标（research aim or objective）。本书的第2章第2节对这几个术语的联系和区别进行了详细介绍，可供参考。此外，第2章中介绍的撰写技巧，这里也适用。接下来，将通过几个具体示例进行详细说明。
下面，将以一篇发表在Sleep Med Rev的系统文献综述为例进行详细介绍（这里仅截取了每个短段落的统领句，topic sentence）。本研究的目的是：“调查分析成瘾与睡眠障碍的相关性”（This systematic review and meta-analysis were conducted to increase our understanding of the relationship betweeninternet addiction and sleep disturbances）。在研究背景中，第一段说明了“近年来，网络的普及性”（Internet use has grown significantly in recent decades）；第二段引出了本研究的主要内容“网络成瘾这一问题的普遍性”［Pathological or compulsive use of the internet（often conceptualized as‘internet addiction’）has an inconsistent prevalence among different populations］；第三段和第四段澄清了“网络成瘾的特点”及“带来的不良后果”（Excessive use of the internet comprises problematic behavior in human interactions with information and communication technologies，and has become a major public health problem）；第五段以一篇既往的文献综述开头，说明了“网络成瘾与精神、心理健康的关系”（In a systematic review，Carli et al.［6］reported the association between pathological internet use and related psychopathology），同时引出了睡眠障碍这一主要内容；第六段中，具体说明了现阶段关于“网络成瘾与睡眠障碍相关性”的研究进展（The excessive use of social media and internet plays an important role in initiating and increasing sleep disturbances within the younger community），这一段也是本研究背景中的核心段落，这里将对其展开介绍（如示例5-7所示）。首先，作者回顾了既往原创性研究结果，发现各个研究的结果均不一致。紧接着，引出了2014年发表的一篇文献综述。在肯定这篇综述的同时，也提出了其可进一步完善的地方；进而顺理成章地引出最后一段。
示例5-7 研究背景第六段
The excessive use of social media and internet plays an important role in initiating and increasing sleep disturbances within the younger community［43］.De Vries et al.found that internet users with psychiatric disorders are more likely to experience sleep problems，depression，anxiety，and autism［20］.Several studies have considered the quality of sleep in people with IA［12，18，44-46］，but in some studies no significant relationship has been found［19］.In studies that have reported a significant relationship between IA and sleep disturbances，the severity of such a relationship has been varied.For example，Kiatzawa et al.reported that university students with problematic internet use reported 52%higher chance of sleeping disturbances than those with ordinary internet use［45］，while Li et al.reported that the chance of having sleep problems in students with IA was three times higher than in normal internet users［47］.A systematic review in 2014 reported an association between online gaming addiction，problematic internet use（PIU），and sleep problems.The results of the study showed that pathological internet use appeared to be associated with a low sleep quality and subjective insomnia［18］.Although this study provided valuable information concerning the relationship between internet use and sleep disturbances，a quantitative meta-analysis of findings has never been conducted on this relationship and the severity of the association remains unclear.
在本研究背景的最后一段，作者提出了开展本综述的重要性、必要性以及研究目的。如示例5-8所示。(https://www.daowen.com)
示例5-8 研究背景最后一段
Considering the importance of IA and its potentially increasing prevalence，further studies are needed to examine related factors and negative consequences.Despite the increasing number of studies on this field，there has been no recent review examining the relationship between IA and sleep disturbances.
Therefore，to summarize available findings and collate more solid evidence for a deeper understanding of the relationship between IA and sleep disturbances，the present systematic review and meta-analysis was conducted.
再以另一篇文献综述为例［这里仅截取了每个段落的统领句（topic sentence）］，本研究的目的是：“调查地中海饮食在非酒精脂肪肝患者中的效果”（the aim of this systematic review is to summarize the effect of Mediterranean diet on serum metabolic indices and anthropometric measures among non-alcoholic fatty liver disease patients）。
第一段，作者对“非酒精脂肪肝”进行了概述（包括定义、患病率、机制、治疗）（Non-alcoholic fatty liver disease is defined as an increased accumulation of triglyceride in hepatocyte either due to increased inflow of free fatty acids or de novo hepatic lipogenesis）；第二段，提出了“治疗性饮食对非酒精脂肪肝的作用”［Over the past decades，several therapeutic diets including dietary approaches to stop hypertension（DASH），Ornish，Atkins，the vegetarian-based and Mediterranean diet（MD）have been investigated in the prevention or treatment of NAFLD］，并着重介绍了地中海饮食；第三段，介绍了“目前关于地中海饮食对非酒精脂肪肝的效果”；最后一段，总结并解释了“现阶段研究结果不一致的原因”，进而引出了开展本综述的原因及内容（Studies that assessed the effects of MD on NAFLD have controversies.These studies used different methods for assessing NAFLD severity and also in different populations.Moreover，relatively small sample size has been used in the majority of the studies assessing this efficacy.To address these issues，we carried out this systematic review by pooling the results from Randomized clinical trials（RCT）studies to examine the effectiveness of MD in the treatment of NAFLD among the adult population.）