2.摘要
摘要的目的是使读者知道：研究做了什么？怎么做？发现了什么？研究结果有何启示？同标题一样，摘要的内容需要简短而丰富。一般情况下，字数在200～300字（因期刊而不同）。不可在摘要中使用引文，减少缩写的使用（有些期刊，不允许在摘要中使用缩写）。一般情况下，摘要会留到最后再写。摘要的格式可以分为结构式摘要和非结构式摘要。这两种类型的摘要撰写方法，具体细节可参考第2章第1节。这里仅对需要格外注意的要点进行介绍。
摘要中能够提供信息的多少，取决于期刊对于摘要字数的要求。但不论字数限制是多少，结构式摘要均需包含研究背景/目的、方法、结果和结论。如示例5-4所示，作者首先介绍了研究背景和目的；继而给出了具体的方法（包括：检索的数据库、涵盖时间、纳入的研究类型）；接着，简要介绍了本研究的主要发现；最后，给出相应的结论和对未来研究的建议。注意：这个摘要的结果中，作者未给出具体的数据（有些期刊要求，不能在结果中给出具体的统计值，例如P值）。在撰写摘要时，要尤其注意这一点。
示例5-4 结构式摘要举例1
Background：Dietary habit can play a key role in the prevention and treatment of fatty liver disease（NAFLD）.Although many studies have investigated the effect of Mediterranean diet on NAFD，findings are inconsistent and there is no systematic review on this topic.Therefore，the aim of this systematic review is to summarize the effect of Mediterranean diet on serum metabolic indices and anthropometric measures among NAFLD patients.
Methods：We searched titles，abstracts，and keywords of articles indexed in Science Direct，MEDLINE，and Google Scholar databases up to October 2018 to identify eligible RCT studies.Randomized clinical trials assessing the effects of MD on NAFLD were included.
Results：The present study included 10 randomized controlled trials，which involved a total of 856 adults with NAFLD.According to the result，MD may improve anthropometric measures，lipid profile.Glycemic indices，liver enzyme，and NAFLD severity indices among patients with NAFLD.
Conclusion：We found that MD could alleviate NAFLD severity parameters but differences between studies should be taken into account.Finally，in order to draw a firm link between MD and NAFLD，more clinical trials with adequate sample size and better methodology should be done.
再如示例5-5所示，本摘要中，作者给出了详细的方法，包括检索的数据库、论文类型、时间段、纳入和排除标准、统计分析方法及PROSPERO注册号。在结果中，提供了具体的数据（包括效应值、可信区间等）。(https://www.daowen.com)
示例5-5 结构式摘要举例2
Methods In this systematic review and meta-analysis，we searched MEDLINE，Embase，the Cochrane Library，and Google Scholar databases for observational studies，systematic reviews，and randomised controlled trials published between Jan 1，2001，and March 31，2017，without language restrictions.We included studies reporting mortality outcomes for international migrants of any age residing outside their country of birth...We calculated summary estimates using randomeffects models.This study is registered with PROSPERO，number CRD42017073608.
Findings Of the 12480 articles identified by our search，96 studies were eligible for inclusion...The summary estimate of all-cause SMR for international migrants was lower than one when compared with the general population in destination countries（0-70［95%CI 0-65-0-76］；P2=99-8%）...Point estimates of all-cause age-standardized mortality in migrants ranged from 420 to 874 per 100000 population.
非结构式摘要虽然没有提供明确的小标题，但需要涵盖的核心内容与结构式摘要相同。如示例5-6所示，作者在摘要中给出了研究背景、目的、方法、结果及结论。
示例5-6 非结构式摘要
The pathological use of the internet-conceptualized as‘internet addiction’-might be crucial in initiating and increasing sleep disturbances in the community.While inconsistent evidence is reported regarding the association of internet addiction and sleep disturbances，the severity of this association remains unclear.【背景】This systematic review and meta-analysis were conducted to increase our understanding of the relationship between internet addiction and sleep disturbances.【目的】A systematic review was conducted through Scopus，PubMed Central，ProQuest，ISI Web of Knowledge，and EMBASE using key-words related to internet addiction and sleep problems.Observational studies（cohort，case-control，or cross-sectional studies）focusing on association between internet addiction and sleep disturbances including sleep problems and sleep duration were selected.A meta-analysis using random-effect model was conducted to calculate the odds ratio（OR）for experiencing sleep problems and standardized mean differences（SMDs）for sleep duration.【方法】Eligible studies（N=23）included 35，684 participants.The overall pooled OR of having sleep problems if addicted to the internet was 2.20（95%CI：1.77-2.74）.Additionally，the overall pooled SMDs for sleep duration for the IA group compared to normal internet users was-0.24（95% CI：-0.38，-0.10）.【结果】Results of the meta-analysis revealed a significant OR for sleep problems and significantly reduced sleep duration among individuals addicted to the internet.【结论】
根据以上内容，在撰写摘要时，提出以下建议：①在撰写“方法”时，可以给出检索的数据库、文献涵盖时间段、纳入的文献类型、主要分析方法（量性的数据统计分析方法或质性的总结方法）、综述注册号。②在撰写“结果”时，对纳入的文献数量进行汇报，对能够反映研究目的的主要结果进行总结。